tragacanth would be less soluble, and a group like agar, for example, would not appear to be soluble at all. It is by no means implied that solubility invariably depends upon differences in the carbohydrate component as it might also result from the character of the aminocompounds or proteins present, expecially in a protoplasm rich in nitrogen.

My studies of growth have been carried out on the assumption that the principal features of importance are those which might be due to the reactions of the carbohydrates and of the proteins which may be present. It is in order therefore to inquire into the condition in which these substances may occur in living matter particularly with respect to their relation to each other. The first and most important relation to be considered is the fact that the mucilages or pentosans and the albumins of amino-compounds of the cell may diffuse into each other very slowly or not at all. Their joint presence in living matter is in a condition in which they are intimately mixed in a colloidal condition. Molecules or groups of molecules of each lie side by side with various possible arrangements. Thus it is conceivable that the mucilage of a cell might be in the form of a mesh or honeycomb with the proteins forming droplets enclosed in the continuous structure, or the reverse might be the case; again substances of both groups might each form a continuous meshwork interlocking with the other, and another category of variables would be introduced by the lipins which might be interposed or incorporated in these systems. Living matter probably does not remain fixed in any one of these simple arrangements, or in any one of a dozen others which might be described if space permitted, and the suggestion is ventured that the play of molecular force where aggregates of a different kind are in contact may constitute the essential and characteristic action of living matter.

Let us now fasten attention upon the theoretical final structure of protoplasm and endeavor to construct for ourselves a mode or plan of action which might be followed in its growth. Growth as has been defined con

sists of two processes. First the molecules or aggregates of molecules of the two kinds, the carbohydrates and the albumins, combine with and absorb water, thus increasing the volume of these units regardless of whether such molecules be in the form of droplets or fibrilla of a meshwork. Instances of growth are known in which water only has been added to the colloidal structure in which in all probability the solid particles have been variously rearranged. In general however growth is accompanied by the accretion of molecules of solid material in such manner that as development proceeds their proportion to that of the water taken increases and organs are then said to show an increase of relative dry weight with age.

On the other hand, my own studies have shown that succulent organs or stems, such as leaves of the Crassulaceae, joints of cacti, fruits, etc., do not show such increase and the proportion of solid matter and of water undergo but little change, their incorporation being at a rate which keeps them near the initial proportion. It is suggested that such action may be shown by the fleshy fungi although I have not seen any data bearing directly upon this matter.

The conditions under which hydration may ensue are by no means identical for the two main constituents of living matter. Thus the albumins and their derivatives as exemplified by the behavior of gelatine show a swelling determined or facilitated by the hydrogen ion concentration or acidity of the solutions, being increased as this rises. The pentosans, on the other hand, show no such increase, and being weak acids, their hydration is retarded by the hydrogen ion. The swelling of a mixture of the two will therefore be a resultant of these effects and of the proportion of the two elements in the living mixture, and as the unceasing action of respiratory metabolism results in the formation of some residues of acids, the condition of hydration of any mass of protoplasm may be said to reach a volume determined by these opposed reactions. The effects in question may be illustrated by the citation of my experiments, in which gelatine

was found to show a swelling in hundredth normal acetic acid fifty per cent. greater than in distilled water, agar forty per cent. less, and a combination of eight parts of agar and two parts of albumin, about forty per cent. less than in water.

The hydrogen ion concentration of the fluids in a plant cell are controlled by the buffer conditions which exist there, but still the range of variation is much wider than that found in the circulatory systems of animals. Bases or cations are seen to affect the swelling of the plasmatic mixtures in my experiments. Various authors having secured results indicative of accelerating effects of certain aminocompounds on growth, some swelling tests of the effects of these substances were made with the discovery that such an amino-acid as glycocoll in hundredth molar solutions seems to retard the swelling of gelatine, at least when the increase in thin dried plates is considered, and to accelerate the swelling of agar to and beyond the total in water. The mixture of agar and albumin, as well as a mixture of agar and gelatine, shows a greater hydration in glycocoll than in water.

The possible physiological significance of these results is heightened by the knowledge of the fact that some of these amino-compounds may be taken to be universally present in growing cells and they probably vary less than the organic acids. It is suggested that the ammonia group in these compounds may form a salt with the carbohydrates with the effect of increasing the hydration capacity. Whether any reaction with, or effect upon, the hydration of the protein element occurs is not yet clear, although it is obvious that such action might be of fundamental importance in nutritive metabolism. The entire matter of hydration may be briefly summarized by the statement that the fundamental properties of a colloidal mixture or of living matter will depend upon the proportion of albumins and of pentosans, and upon the properties of the particular substances of each group which may be present. Hydrogen ions within the possible range of concentration increases hydration of the albuminous substances and depress that of

the pentosans. Bases or cations exert a reverse effect on the albuminous substances and depress hydration of the pentosans slightly. Certain amino-compounds depress the swelling of albuminous compounds, but facilitate the hydration of pentosans and sections of such substances when mixed in a proportion of four to one with albumin undergo hydration to a degree equivalent to cr even greater than that in water.

The second phase of growth, that of the incorporation of molecules of solid matter is not so easily described since it is not so directly susceptible of experimental test. If the conception of the pentosan-albumin composition of protoplasm is correct, it is obvious that the mass of living matter may not be increased simply by the addition or diffusion of sugars into the meshwork, as is supposed by some writers.

Before the material in these carbohydrates may actually become a part of the colloidal living mesh it is undoubtedly broken down to some extent by enzymatic or respiratory action, part of the material being carried through transformations to organic acids or carbon dioxide, some of the material is combined with the ammonia group (NH) to form amino-compounds, some with the lipins, while some of these sugars may be converted to the pentose form in which they would so markedly affect the hydration capacity of the mass.

By way of crude illustration, protoplasm might be regarded as the wick of a lamp which draws sugar into its meshes, burns the sugar and in the burning some of the sugar not completely consumed unites with other substances to form additional fibers of the wick. At this point it would be well to divert attention for the moment to the so-called “nutrient" salts, the presence of which in the soil and in the liquids of the plant is so indispensable to the plant. It is necessary for an understanding of the real nature of growth to have clearly in mind that living matter is a colloidal mixture of proteins and carbohydrates, which takes up water and gains solid material in growth by processes which are actually retarded by these salts. These com

pounds in fact yield no energy and furnish no building material. They may act as catalyzers or as releasing agents, and as controls of water absorption or as guides in colloidal arrangement, but they are not "food-material" in any sense. The constituents of fertilizers should be designated as "culture salts" and as such have all of the importance which has been imputed to them; a determination of the composition and proportion of salts in a culture solution which will induce maximum production of grain, fruit or forage is a problem of the first rank now happily receiving something like an adequate investigation.

The foregoing suffices to account for the mechanics of growth or expansion of a singlecelled or naked organism. The development of complex, massive or higher organisms especially in plants, however, is accompanied by the formation or deposition of an outer layer of denser consistency which occurs at any phase boundary of colloidal material. This membrane so-called is in any case a product of the surface energy of the mass or system of living material in the cell and of the material in contact and its constitution, and even its structure must vary as widely as that of the protoplasm which produces it.

External to the membrane is the cell-wall which begins to be formed around plant cells as soon as they divide or are separated and this wall increases in rigidity and offers greater resistance to stretching as it grows older.

The arrangement in question, therefore, is one in which the expanding and growing protoplast is enclosed in a sac or bag of its own making and which acts as a screen not only in allowing some materials to pass while others are shut out, but also is so constructed that some solutions pass through it more readily into the cell than out of it, these being simply examples of some of the many facts discussed under the designation of permeability. The external screening membrane takes on a special significance in connection with the osmotic action of the vacuoles.

These sacs were at one time thought to have a morphological value, but it is now understood that almost any hydrating colloidal mass

may exhibit syneresis in which cavities or canals are formed in which the colloidal material accumulates in an attenuated or liquid condition. These syneretic cavities increase by absorption of water and by the time the protoplasm of the cell has attained about half of its ultimate bulk in some instances, these cavities have enlarged to occupy a space as large as the protoplasm and acting as vacuoles by which they are ordinarily known, eventually fill a much larger space. The expansion of these vacuoles and the consequent increase in volume of the cell constitutes part of the enlarging action of growth, and this expansion takes place by the force of osmotic action. and the result of such stretching is to set up a tension ordinarily designated as turgidity. The vacuoles continue to hold some of the colloidal material and may also carry in solution almost any substance in the cell which may be passed into them by osmosis or diffusion, including sugars, salts, acids, aminocompounds, etc.

The enlargement of the individual masses of living cells in organisms entails a certain amount of work which in the earlier stages is derived almost entirely from imbibition or adsorption, and while such action continues throughout the growth or life of the living matter, there is in addition the stretching action exerted by the expanding vacuoles by osmotic action. The growing regions or plants at all times include cells in all of these stages, from the newly separated protoplasm which is expanding entirely by imbibition of water and incorporation of new material, others in which the syneretically formed vacuoles are increasing and thus adding to the volume of the cell by osmotic action, and others approaching maturity in which the vacuole may have attained such size as to occupy many times the space of the living matter which may indeed now be but a sac with its layers of irregular thickness lying internal to the wall, which now has become dense and rigid.

The measurement of the growth of a stem, root or fruit of a plant will, therefore, show the composite changes in volume of cell masses

in all of these stages, and consequently express the action of imbibition and osmosis.

The distinct action of imbibition and the later joint action of hydration by osmosis and by imbibition may be most readily recognized, in organs in which the region of growth is generalized as in the ovate flattened joints of Opuntia or in such globular fruits as the tomato. The measurement of the growth of one of these joints may be begun when it has a lateral area no larger than the thumbnail, and during this stage the increase is rapid and shows a minimum disturbance from changes in external conditions, as shown by the illustrations. Growth continues throughout the entire mass until an advanced stage of development is reached, when it first slackens in the basal portion. By this time large vacuoles have been formed in the thin-walled cells, and water loss from the surfaces of the organ has reached such a rate that great daily variation in the volume results and actual shrinkage may en

sue.

A similar history may be predicated for such structures as the large berry-like fruit of the tomato, it being noted that the material in both illustrations takes on solid matter and water at such rate that not much alteration in their proportions occurs during development.

The enlargement of the trunk of a tree results from the multiplication and growth of cambium and other cells on the outside of the trunk directly inside and covered by the bark. The trunk of the tree is in effect a cylinder of moist but dead woody tissue surrounded by a living sheath which becomes very active at some time in the year and which as a result forms an additional layer or sheet of wood on the trunk which in cross section gives the appearance which has caused it to be designated as an annual ring of growth.

The actual course of growth or formation of these annual cylinders or, more strictly speaking, cones, has not until recently been measured. In 1918 I was successful in making a working model of a dendrograph which might be attached to the trunk of a tree in such manner that its changes in volume due to whatever causes were traced on a ruled sheet of paper carried by a revolving drum. The

essential part of this apparatus is a yoke of metal; which has two bearing screws resting on the trunk and carrying a third contact point on the end of the pen lever. It was not possible to make a practicable instrument until a yoke could be constructed which showed but little variation as a result of changes in temperature. Three alloys with a very low temperature coefficient, bario C., manganin and invar have been used and dendrographs are now in operation on the trunks of two species of pine, and oak, an ash, a sycamore and a beech tree, and as these instruments were placed in position before growth began in 1919, there is every prospect that seasonal records will be obtained from which the principal features of growth may be seen. Weekly records show that these trees do not behave alike and that many conditions are to be considered in interpreting the records.

It is evident for example that but little is known concerning the properties of bark as a water-proofing or protecting coat for the tree. The loose bark of the ash and pine trees seems to allow such a great water loss from the surface during the mid-day period as to cause actual shrinkage which does not occur in trees such as the beech and live-oak, which have a perfect living green outer bark or skin. The facts disclosed by these records can not fail to be of interest in a discussion of any phase of the complicated problem of the ascent of sap.

D. T. MACDOUGAL
DESERT BOTANICAL LABORATORY

JOSEPH BARRELL AMERICAN geology has lost one of its foremost leaders, one who promised to stand as high as the highest. Professor Barrell's other colleagues will undoubtedly agree with Professor T. C. Chamberlin when he says: "We had come to look upon him as one of the most promising leaders in the deeper problems of earth science. We feel that his early departure is a very sad loss to our profession not only, but to the whole group of sciences that center in the earth and its constitution."

Only a few days before his death there came to him the news of the highest honor that can be given to an American scientist, election to the National Academy of Sciences. His election, furthermore, was by a unanimous vote of the academicians present at the April meeting in Washington, and such a vote is rare in the academy.

This

Joseph Barrell, the son of a farmer, was born at New Providence, N. J., December 15, 1869, and died of pneumonia and spinal meningitis in New Haven on May 4, 1919. He leaves a wife and four sons. Standing 5 feet 10.5 inches in height, of the blue-eyed Nordic type, with a full head of wavy light-brown hair, he was spare and slender in build, but characterized by great muscular strength in comparison to body weight. He was of the eighth American generation from the Puritan George Barrell, who migrated from Suffolk, England, and settled at Boston in 1637. first American Barrell began as a cooper, but most of his descendants have been sea-going people and shipping merchants. The most widely known and wealthiest was Joseph Barrell of Boston, after whom the subject of our sketch, his great-grandson, was named. This Joseph Barrell is said to have "early espoused and firmly maintained the cause of his country," and for a time represented the town of Boston in the State Legislature. It was in his splendid home that General George Washington was entertained during his visit to Boston.

Professor Barrell received the first part of his collegiate education at Lehigh University, taking in due course its B.S., E.M. and M.S. degrees, and in 1916 this institution gave him its doctorate of science. From 1893 to 1897 he was instructor in mining and metallurgy at his alma mater, and then was given leave of absence to go to Yale for graduate studies in geology, taking his Ph.D. degree in 1900. Returning to Lehigh, he was made assistant professor of geology, and for three years taught not only geology but zoology as well. In 1903 he was called to Yale as assistant professor of geology and in 1908 promoted to the chair in structural geology. In the geological department at Yale he was a unifying force

and a tower of strength. During the summer months from 1893 onward, Barrell spent nearly all the time in the field, working at first as an engineer in the coal mines of Pennsylvania, then in the mines of Butte, Montana, devoting one summer to the geology of southern Europe, and later studying widely the geology of the Appalachians and of the New England States.

Professor Barrell's first publications, in 1899 to 1900, deal with mining, but since 1901 nearly all his work has been in geology. His bibliography has upward of forty-five titles, totalling more totalling more than 1,500 pages. Several articles remain unpublished, at least two of which it is hoped to print during this year. more detailed account of his life and work will appear in an autumn number of the American Journal of Science.

Barrell's most important work has to do with the strength of the earth's crust. The series of papers bearing that title examine into "the mechanics of the earth considered as a body under stress, owing to the variation in density and form which mark its outer shell." He was all the more able to handle this most difficult subject because of his thorough training in engineering at Lehigh. His last work along this line will be published this fall. From the manuscript we learn that "The larger features of the earth's surface are sustained in solid flotation, and at some depth the strains due to the unequal elevations largely disappear, the elevations being compensated by variations of density within the crust. In consequence, the subcrustal shell is subjected to but little else than hydrostatic pressure." Isostatic balance is, however, not everywhere in adjustment, but the adjustments are held to be irregular and imperfect in distribution and mostly concentrated in the outer one hundredth of the earth's radius, with a tendency to progressively disappear with depth. On the other hand, "the outer crust is very strong, capable of supporting individual mountains, limited mountain ranges, and erosion features of corresponding magnitude."

Barrell also did much toward working out the criteria by which the climates, marine