The form of the frequency distributions for two of the lines is shown in diagram 3. The epicotyl of the hemitrimerous is in essentials of anatomy identical with that of the dimerous seedling. Not only are there marked differences in the actual number of bundles, but the variability of bundle number changes from region to region of the seedling, and differs in the three seedling types. Whether judged by range, standard deviation or coefficient of variation, the variability of bundle number in the central region of hypocotyl tends to be distinctly higher in the dimerous than in the trimerous plantlets; but in the epicotyl just the reverse is true, the variability of the trimerous plantlets exceeding that of the dimerous. These differences are conspicuous in diagrams 2 Percentage frequency distribution of number of bundles in central region of hypocotyl in dimerous and trimerous seedlings. Abscissae represent bundle numbers, ordinates represent percentage frequencies. and 3. In the first case it is the dimerous plantlets, in the second case it is the trimerous ones which show the greater variability. Apparently this is due to differences in the number of intercalary bundles in the hypocotyl, and to the extent of division of the bundles in the epicotyl, of the two types of seedlings. The coefficients of correlation between various bundle systems also differ widely. In both trimerous and dimerous seedlings there is a negative correlation between the number of primary double bundles and the number of intercalary bundles at the base of the hypocotyl. Thus the number of intercalary bundles is smaller in seedlings with larger numbers of primary double bundles and vice versa. This result for seedlings of the same (external) morphological type is in agreement with those obtained by a comparison of seedlings which are externally dimerous and trimerous, since the latter frequently have a larger number of primary double bundles but a smaller number of intercalary bundles than the former. In both types of seedlings variation in the number of intercalary bundles is the primary factor in determining variation in the total number of bundles at the base of the hypocotyl. Turning to the problem of the interrelationship of bundle number at different levels in the seedling we find that there is a substantial correla Percentage frequency distributions of total bundle number in the central region of the epicotyl of dimerous and trimerous seedlings of two lines. Abscissae represent bundle numbers, ordinates represent percentage frequencies. tion between the numbers of the three classes of bundles-primary double bundles, intercalary bundles, and total bundles at the base of the hypocotyl and the number of bundles in the central region of the hypocotyl. In the normal seedlings the coefficients average +0.509 for number of primary double bundles and number of hypocotyledonary bundles, +0.629 for intercalary bundles and hypocotyledonary bundles, and +0.813 for total bundles and hypocotyledonary bundles. In the trimerous plants these correlations average +0.381, +0.238 and +0.598, respectively. The correlations for normal plantlets are practically without exception higher than those for abnormal seedlings. The correlations between the number of bundles in the hypocotyl (both basal region and central region) on the one hand and the number of bundles in the central region of the epicotyl on the other differ conspicuously from those found between the numbers of bundles at the two levels in the hypocotyl itself, in that the coefficients are extremely slight. They are positive in some series, but negative in others. The regression straight lines and the empirical means for number of bundles in the hypocotyl (lower line) and epicotyl (upper line) associated with various numbers of primary double bundles at the base of the hypocotyl in two of the lines is shown in diagram 4. The irregularity of the means is at least in part due to the fact that the frequencies are largely concentrated in the two classes of 4 and 5 primary double bundles. The Regression of number of bundles in central regions of hypocotyl and of epicotyl on number of primary double bundles at base of hypocotyl. Abscissae represent primary double bundles, ordinates represent mean number of bundles in hypocotyl and epicotyl. slope of the line representing change in hypocotyledonary bundles associaated with variation in number of basal bundles is steep, showing a rather close dependence; but the line showing the change in epicotyledonary bundles associated with the same variations in basal bundles is very slight, showing the laxness of the interdependence of bundle number in these two regions. On the basis of the data available it is impossible to assert that there is any relationship at all between bundle number above the cotyledons and bundle number below them. These results indicate that there is a complete reorganization of the vascular system at the cotyledonary node. It will be evident from the foregoing outline that the vascular structures of the seedling are not constant but are highly variable, even within genetically very homogenous material. It is quite possible, therefore, that anatomical investigations based on but a few sections for each species might lead to erroneous results. Seedlings differing in external form are differentiated in their internal anatomy. Such differentiation is evident not only in mean number of bundles but in the degree of variability in bundle number. Thus, in normal seedlings the variability is higher in the hypocotyl than in the epicotyl, whereas in seedlings with three cotyledons and three primordial leaves just the reverse is true. The external form and the internal structure of the seedling are highly but not perfectly correlated. Finally in both normal and variant seedlings, the number of vascular elements of the several regions of the seedling are correlated in very different degrees; the correlation between some is high; between others it is practically wanting. Papers to appear in the American Journal of Botany may be consulted for details. 1 The values given in each case are the maximum and minimum constants for the lines investigated. For the trimerous and dimerous seedlings all the averages are based on five lines. For the hemitrimerous seedlings the averages for primary double bundles and intercalary bundles are based on five lines while for the mid-region of hypocotyl and the mid-region of epicotyl they are based on six lines. Data for number of root poles are available for only three lines. 2 Because of the extreme rarity of hemitrimerous seedlings it is not feasible to discuss variability of bundle number in this group. THE PRESENT STATUS OF THE LONG-CONTINUED PEDIGREE CULTURE OF PARAMECIUM AURELIA AT YALE UNIVERSITY BY LORANDE LOSS WOODRUFF OSBORN ZOOLOGICAL LABORATORY, YALE UNIVERSITY Communicated by R. G. Harrison, December 30, 1920 As a matter of record it seems advisable to bring up to date and summarize the chief results derived from the writer's main pedigree culture of Paramecium aurelia. This culture, designated Culture I, was started on May 1, 1907, by the isolation of a "wild" individual which was found in a laboratory aquarium.1 The original specimen was placed in about five drops of culture fluid on a glass slide having a central ground concavity, and when this animal had produced four individuals, each of these was isolated on a separate slide to form the four lines of the culture. The four lines have not been kept distinct from one another throughout the work, but have been replenished by cells from one of the sister lines when, through accident or otherwise, one or another of the lines has become extinct. The culture has been maintained by the isolation of a specimen from each of these lines practically every day, with the exception noted below. The number of divisions in each line has been recorded at the time of isolation and the average rate of these four lines has again been averaged for varying numbers of days (5, 10, or 30 days) as the exigencies of the different experiments demanded. These data have afforded the graphs of the division rate. Permanent preparations have been preserved from time to time for the study of the cytological changes during the life history. During the first eight months of the work the culture medium consisted of infusions of hay and fresh grass, but from February, 1908, to the present time various materials collected from ponds, swamps, etc., have been employed. The infusions were thoroughly boiled to prevent the contamination of the pure culture with foreign strains of Paramecium. In short, the cells of the four lines of the culture to-day are direct lineal descendants by division of the single animal isolated in 1907. The object of starting the culture was to determine whether Paramecium can reproduce by division indefinitely without recourse to conjugation. Throughout the work the possibility of conjugation in the four lines of the culture has been precluded by the almost daily isolation of the products of division. Accordingly its continued life and health has long since justified the conclusion that conjugation, involving syncaryon formation, is not, as previously generally maintained, a sine qua non for the continued life of Paramecium, in particular, and, presumably, of Infusoria in general. At the completion of the The vertical Graph showing the rate of reproduction of the pedigree race (I) of Paramecium aurelia during the first eight years of culture. |