356 president's address. — section d 



identification of mutants already known, in the production of hitherto 

 unknown mutants, and in extending our knowledge as to the bearing 

 of saltatory action. They also verified De Vries' experiments, 

 showing that certain mutants are " fixed," and are not swamped by 

 crossing with the parent type. Thus the view is confirmed that 

 mutation is a real factor in Evolution. 



But, for our present purpose, the most important part of the 

 research is that which bears on the induction of mutations and the 

 heritability of induced characters. 



The plan followed was the injection into the developing ovary of 

 dilute solutions of mineral salts or solutions of other substances. 

 With several plants negative results were obtained. 



An ovary of Oenothera biennis thus treated with dilute zinc 

 sulphate yielded mutants of the usual kinds, and in the proportions 

 usual in this plant, about 0*5 per cent, of the whole progeny. A single 

 specimen of an unknown mutant appeared, and its characters were 

 found to be fully transmissible. Too much importance must not be 

 attached to this appearance, since " the probability must be taken into 

 account that it may be a mutant of rare occurrence, the cycle of which 

 oame within the experiments." 



The most interesting results were obtained with Raimannia 

 odorata, an Evening Primrose from Patagonia. Stimuli of various 

 kinds were applied, and a particular mutant, not known in natural 

 conditions, was obtained in different experiments, irrespective of the 

 kind of stimulus applied, whether injection of a 10 per cent, sugar 

 solution or of a 0*001 per cent, solution of calcium nitrate, or whether 

 the action of a radium pencil. " The atypic forms transmit their 

 qualities perfectly from generation to generation, and the third genera- 

 tion now in hand are like the first from which they came originally " 

 (p. 64). 



With regard to MacDougal's results, Klebs, in his essay in the 

 Darwin Centenary Volume, suggests that the same end might be gained 

 by altering the foodstuff conducted to the sexual cells. And we know 

 that cultivation frequently throws plants that constitute in normal 

 conditions quite stable species into a state in which many variants arise, 

 some of which may prove to be elementary species. 



In comparing the results of Tower and MacDougal, we must bear 

 in mind that MacDougal considers that the stimulus was not in most 

 cases applied until the formation of the germ cells was complete ; 

 whereas, in the case of Tower's experiments, the abnormal environment 

 acted on the maturing germ plasm. 



That the fertilized ovum is not noticeably affected during its de- 

 velopment by the special character of the soma in which it is lodged and 

 by which it is nourished has been sufficiently demonstrated. Thus 

 Heape (Proc. Roy. Soc, V. 48 and V. 52) has described the results of 



