466 



SCIENCE 



[N. S. Vol. XLVII. No. 1219 



tants. In nature, where, as a rule, mutations 

 are very rare, the chance for the occurrence of 

 full mutations is mostly too small, and stray 

 novelties, found in the field, must generally 

 have originated in the indirect v?ay of half 

 mutants followed by mass mutation. This 

 would, at the same time, explain why they are 

 so often met with in two or more individuals. 



Half mutants may differ externally from the 

 strain, which produced them, as e. g., in the 

 case of (Enoihera rubrinervis, or may fail to 

 show such visible marks, as in that of 0. 

 LamarcJciana gigas mut. nanella. In both 

 cases they will give rise to the full mutant in 

 relatively large numbers in the second gen- 

 eration. The full mutant of the first instance 

 is designated as 0. mut. deserens, and that of 

 the second is represented by dwarfs with the 

 flowers, foliage and nuclei of 0. gigas. They 

 occur in about 20-30 and 15-18 per cent, 

 among the offspring of the original half mu- 

 tants. 



In a strain of ordinary com, which I culti- 

 vated for other purposes, an instance of mass 

 mutation has occurred which evidently re- 

 quires the same principle for its explanation. 

 The mutants have been described under the 

 name of Zea Mays sterilis and figured in Vol. 

 I. of the Botanisch Jaarboeh of the Society 

 Dodonsea at Ghent in Belgium. They are 

 devoid of all branches. No lateral stems, no 

 ears, no ramifications of the spike and no 

 male flowers are produced. The whole plant 

 is a barren stem with a naked spill instead 

 of an inflorescence. They are built in the 

 same manner as the unbranched fir, Pinus 

 Ahies aclada, described and figured by 

 Bchrbter. 



I cultivated my strain after a simple 

 method, sowing each year the seeds of a single 

 ear, planting the seedlings on sufficient dis- 

 tances to insure a high degree of self-fertili- 

 zation and eliminating the individuals pro- 

 duced by stray crosses by means of vigorous 

 selection. No unbranched specimens occurred 

 during the six first years. In the seventh gen- 

 eration, however, they appeared unexpectedly 

 and in 40 specimens among 340. This in- 

 dicated a percentage of 12, which is far 



higher than the ordinary mutability in Lin- 

 aria, Chrysanthemum, CEnothera a. o. (mostly 

 1-2 per cent.). Besides these unbranched 

 plants some intermediate forms were seen, 

 with incompletely developed ears and spikes. 

 I chose one of these for the continuation of 

 the race and had, next year, a generation of 

 57 individuals eleven of which belonged to 

 the new type. The percentage figure was 19, 

 giving new proof of the occurrence of mass 

 mutation. 



If we assume a sexual cell of the fifth gen- 

 eration to have mutated into the unbranched 

 character, and to have combined with a normal 

 one, the sixth generation may have included a 

 half mutant of the new type, which could not 

 be discerned at the time, since it was wholly 

 miexpected, but was chosen by chance. Segre- 

 gating after the principle of Bartlett it could 

 have produced 25 per cent, of sterile individ- 

 uals, besides 50 per cent, of half mutants with 

 more or less incomplete ramification. These 

 would repeat the splitting in the following 

 generations. Had I known that principle at 

 the time, I would surely not have given up 

 the culture, as I did. 



In the production of other sterile vari- 

 eties the principle of mass mutation must 

 have played a similar role. They can not 

 evolve through the slow accumulation of small 

 useful deviations, and their chance of arising 

 at once as full mutants must be very little. 

 Double flowers of the petalomanous type are 

 well-known instances. I once found such a 

 mutation of Ranunculus arvensis in a meadow, 

 and the corresponding variety of Caltha pa- 

 lustris is cultivated in gardens, where it propa- 

 gated in the vegetative way. 



Yellow seedlings, which die after unfolding 

 their seed-leaves, are another instance, and 

 for these the mutational percentages are easily 

 ascertained. They are often high enough to 

 give proof of the presence of mass mutation. 

 I found 25 per cent, for Linaria vulgaris, 

 15—30 per cent, for Papaver Bhoeas, 10-15 per 

 cent, for Scrophularia nodosa, 9—13 i>er cent, 

 for Clarlcia pulchella and about 10 per cent, in 

 some other instances. 



Mass mutation must be quite common in 



