KNOWLEDGE OF THE MIJTATIKG OENOTHEEAS. 37 



fully developed. One plant of this culture, however, corresponded in all respects with 

 the 0. lata of DeVries, having the characteristically distorted buds and sterile anthers. 



It is now clear that lata possesses 15 chromosomes in some at least, and probably in 

 all individuals. The presence of the extra chromosome is probably the cause of the 

 failure in the pollen development. The varying distributions of the odd chromosome in 

 the megaspores, and perhaps also partial apogamy, probably account for the inconstancy 

 of the offspring from this mutant. The chromosome-number of semilata is not yet 

 known, and the problem regarding the relation between the extra chromosome and the 

 lata characters therefore remains to be solved. 



If one thinks of the lata characters as emerging from those of O. ZamarcMana, and 



* 



the semilata characters as only half emerged, one gets a picture of the relationships of 

 these three forms. 



O. semilata is one of the rarest of the mutants, having appeared only three times 

 in DeVries's cultures, and every time from O. lata. One such mutant self-fertilized 

 gave 358 plants, all of which were semilata except three which were nanella and four 

 lata. In a cross, O. lata X O. semilata gave 105 plants distributed as follows : 

 61 Lamarckiana, 39 lata, 2 nanella, 2 ohlonga, 1 alhida, which is similar to the result 

 obtained when other forms are used to pollinate 0. lata. 



I obtained four plants showing the characters of 0. semilata in a culture of 75 plants 

 from 0. lata X O. LamarcJciana. The offspring were as follows : — 63 0. LamarcJciana, 

 4 O. lata, 2 O. lata nanella {?)y 2 0. semilata^ 1 0. laevifolia (?) , and 3 aberrant 

 rosettes, 2 of which were probably 0. semilata. The kaleidoscopic fluctuations of 

 these plants during their ontogeny often renders their determination a matter of great 

 difficulty. The Eg from one of these self-fertilized 0. semilata plants produced 40 very 

 variable rosettes. About 11 of them were O. semilata, but the rest formed a continuous 

 series running to 0. LamarcJciana and could not be more accurately determined. Three 

 which came into bloom were all clearly 0. semilata. The other O. semilata plant 

 produced in Pg only three plants, all of which were 0. Lamai^chiana. 



O, semilata is only known as a mutant from 0. lata, unlike most of the other mutants 

 which have appeared from various ancestors. As DeVries has stated, its external 

 characters suDrsrest that it is an intermediate hybrid between O. lata and O. LamAircJciana^ 

 and the fact that its offspring breed true does not exclude this interpretation. The fact 

 that O. semilata has only occurred from the single source, O. lata X O. Lamarckiana, 

 supports the view that it is such an intermediate hybrid, rather than a mutant, but 

 its chromosome number may explain why it originates only from O. lata. 



My castration experiments with O. lata (1909 b) have furnished an indication that 

 some form of apogamy occasionally, though rarely, occurs in this mutant. It seems 

 possible that perhaps 1 per cent, of the ovules will develop seeds without fertilization, 

 though the remaining ovules require fertilization for their development. 



The characters of the other mutants from 0. Lamarckiana, which have been less 

 thoroughly studied, wiU not be discussed here. The data presented in this section are 



