272 MISCELLANEOUS STUDIES 



with the position of the leaves on the plant. In the crenate-leaved 

 type this character is much accentuated, as can be seen by comparing 

 figure 14 with figures 1 and 3 ; a warm greenhouse (fig. 14, upper line) 

 gave very marked serration, while a cool greenhouse (lower plant, and 

 also fig. 15) produced leaves much more nearly entire. 



Under the much more extreme conditions of insolation, temperature, 

 and humidity at Riverside, this type was often much dwarfed in com- 

 parison with Snowflake (figs. 16 and 17; see also fig. 23). In general, 

 growth is weaker than with Snowflake and the stems more slender. 

 Buds and flowers are often produced in great abundance, but the 

 capsules are relatively few, small, and few-seeded. See tables 12 and 

 13 for internode data. 



The progeny tests (table 29) show a slightly higher proportion of 

 mutant-type progeny than occurred with smooth-leaved. A striking 

 new feature appears for the first time in these results, the regular 

 presence of linkage, or an association simulating linkage, with the 

 single-double allelomorphs. Further, in all the four apparent mutants 

 tested the crenate factor seems to be coupled with singleness, while 

 among the sixteen F 1 and F 2 crenate parents there seem to be no 

 crossovers. 17 We seem to be justified, for reasons just given, in 

 summing the progeny as in the tables. Two things appear at once in 

 table 29 : ( 1 ) there is a great excess of total doubles over the usual 

 53 per cent; (2) there is a much greater excess of doubles with Snow- 

 flake than of singles with crenate; (3) the supposed double-recessive 

 class (Snowflake double) is about two and one-half times as large as 

 the double-dominant class (crenate single). 



Table 30 adds two features of special interest. First, there is good 

 evidence of selective elimination with poor germination ; compare the 

 remaining percentages with those for "Ithaca, field," "1915," "P 1? " 

 and "Germination poor," and see tables 39 and 40; the only excep- 

 tional case is the low percentage for the thirty plants of 1915-16. It 

 would be surprising if the slow and weak growth of the crenate plants 

 did not lead to such a result. Second, there is evidence that the 

 crenate individuals are smaller than Snowflake even before germina- 

 tion. The seeds of crenate parents are less uniform in size than those 

 of Snowflake parents; small seeds are numerous, and even the larger 

 ones probably weigh decidedly less than normal Snowflake seeds. 

 With five crenate parents included in the cultures of 1913, random 



17 With four of the parents the tests are obviously entirely inadequate; one 

 other, 22d-9, gives no indication of linkage among nineteen progeny. 



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