Babcock and Lloyd: "Somatic Segregation" 



85 



persistent. This ratio was taken to be 

 3.7:1 which was considered a fairly 

 close approximation to the theoretical 

 Mendelian monohybrid ratio. This in- 

 correct statement of the frequency-ratio 

 makes the deviation from the ideal 

 appear much larger than it really is. 

 When calculated on the basis of fours, 

 the ratio of the relative frequencies is 

 3.15:0.85. But even when stated cor- 

 rectly, this ratio has a highly significant 

 deviation from the theoretical ratio in 

 view of the large nimiber of individuals 

 examined. Had the ratio of the fre- 

 quencies of entire fruits (2.8:1.2) been 

 considered, the deviation would not 

 have been quite so serious. Yet even 

 here, the deviation is 12.5 times the 

 probable error, so that the odds against 

 such a deviation occurring where the 

 laws of simple sampling prevail, as they 

 do in normal Mendelian inheritance, are 

 approximately 1,155,000,000,000,000 to 

 1. Hence the observed frequencies are 

 hardly attributable to conditions pre- 

 vailing under the laws of simple samp- 

 ling. Therefore, if we attach any 

 significance whatever to the observed 

 ratios of persistent to deciduous lobes 

 we must infer that this case of appar- 

 ently alternative, discontinuous varia- 

 tion can be explained more reasonably 

 on some basis other than the existence 

 of a segregation-mechanism in soinatic 

 cell division. 



However, too much importance must 

 not be attached to even as decisive a 

 mathematical objection as the present 

 case affords. It must be remembered 

 that in hybrid progenies, wide deviations 

 sometimes occur in the observed fre- 

 quencies of characters which exhibit 

 clear cut alternative inheritance. For 

 example, Collins and Kempton^ obtained 

 an average ratio in a series of crosses 

 between Chinese corn with waxy endo- 

 sperm and American varieties with 

 horny endosperm that displayed a 

 deviation from the expected ratio of 

 over nine times the probable error, 

 which might not occur oftener than 

 once in over a million times under the 



conditions of simple sampling. Yet 

 the two characters are "definitely alter- 

 native, the seeds being either waxy or 

 horny, with no intermediates." 



EXAMINATION OF NEW MATERIAL 



The question then arises : What is the 

 real nature of these phenomena of 

 persistency and deciduousness of calyx 

 lobes in apples and pears? Can evi- 

 dence be found that will throw light on 

 the conditions which induce them? 

 Upon examining several fresh fruits 

 obtained in August, 1916, through the 

 courtesy of Prof. V. R. Gardner from 

 the trees of the Le Conte pear and 

 Transcendant crab that Tufts studied, 

 we have found that when separation of 

 calyx lobes takes place the method is 

 identical with that which occurs when 

 the stamens are loosened. The cells in 

 the basal portion of the calyx lobe fail 

 to grow as rapidly as the cells of the 

 subjacent tissue. In consequence, the 

 epidermis is ruptured near the base of 

 the lobe, peridermal activity super- 

 venes, the deeper tissues are gradually 

 transformed into corky tissue and the 

 lobe finally falls away. In other words, 

 exfoliation of the cal^oc lobes occurs 

 when two conditions are fulfilled, viz, 

 (a) when there is little or no secondary 

 thickening of the calyx lobes them- 

 selves and (b) when there is sufficient 

 secondary growth in the parenchyma 

 underneath the bases of the calyx lobes 

 and at right angles to their axes. In 

 the photomicrographs shown herewith, 

 the antithetical conditions are clearly 

 shown. Fig. 11, 1 is a longitudinal sec- 

 tion through a persistent calyx lobe and 

 adjacent ovary wall of Transcendant 

 crab, showing secondary thickening 

 of the base of the lobe and a conspicuous 

 zone, triangular in cross-section, of 

 small cells which is nearer the bottom 

 of the basin than the points of insertion 

 of the stamens. In marked contrast 

 to this zone of small cells are the large 

 cells of the second growth parenchyma. 

 Fig. 11,2 shows the location of the base 

 of the filament of an exfoliated stamen 



* Collins, G. N., and Kempton, J. H. Inheritance of Waxy Endosperm in Hybrids of Chinese 

 Maize. In 7F Conf. Internal. Genetique, Paris, Compt. Rend, et Raps., 1911, p. 356. 



