Makch 8, 1907] 



SCIENCE 



379 



is not more theory or discussion, but more 

 observation and experiment. I believe that 

 the chromosome theory as applied to the 

 sex problem presents a sufficiently plausible 

 face to be taken for a time as a guide to 

 further examination of the facts. Per- 

 chance the true explanation may be found 

 on the way, even should our working hy- 

 pothesis prove a false leader. 



Edmund B. Wilson 

 Columbia University 



SEX-DETEKMINING FACTORS IN PLANTS 



It is generally agreed that no true sex- 

 determining factors for plants have as yet 

 been recognized, and naturally a botanist 

 would hardly choose the topic which has 

 been assigned to me in this discussion. 

 Claims are, however, constantly made that 

 this or that environmental influence has 

 been observed to modify slightly at least 

 the percentage of the sexes in dioecious 

 plants. The extensive literature of such 

 experiments and observations was summar- 

 ized very fully and critically by Stras- 

 burger in 1900, and I need only allude to it 

 here. 



A great variety of factors have been 

 tested both singly and in combination, but 

 without positive results. Conditions of 

 nutrition, as to both kind and amount, have 

 been exhaustively studied and reports of 

 success in influencing the sex ratio by this 

 or that fertilizer are constantly made, and 

 quite as constantly fail of confirmation. 

 Laurent has recently (1903) claimed that 

 an excess of nitrogen or lime favors the de- 

 velopment of males in spinach, hemp, etc., 

 while potash and phosphoric acid favor the 

 development of females, but his results are 

 not convincing. 



Temperature, light and moisture condi- 

 tions, relative age of parents, relative ma- 

 turity of pollen, early and late planting, 

 pruning, etc., have all been more or less 



elaborately tested without achieving re- 

 sults. 



Gallardo (1901) reported that wild fe- 

 male plants of Dioscorea and Clematis, 

 when transplanted into the botanic garden 

 at La Plata, became hermaphrodite the 

 next year, and the year following returned 

 again to the female condition. The experi- 

 ment was repeated the following year, with 

 the same results, but it is hardly clear just 

 what factor or factors were here concerned, 

 and it is certain that transplanting gener- 

 ally has no such effects. 



That the sex of seed plants can be 

 changed by environmental conditions is, 

 however, further shown beyond the possi- 

 bility of question by the case of the anther 

 smut {Ustilago violacea) which infects the 

 campion (Lychnis dioica L.). Here the 

 fungus, when present in the female plants, 

 regularly leads to the development of sta- 

 mens and the suppression of the pistil. 

 The capacity to develop stamens must, in 

 this case, be assumed to be present in the 

 female plant, and the fungus is able to 

 induce the conditions necessary to their 

 formation and the suppression of the pis- 

 tils, and thus provide for the development 

 of its own spores. Elaborate experimental 

 attempts by Strasburger to duplicate on 

 uninfected plants the effects produced by 

 the parasite led, however, to no results. 



In the absence of positive data as to sex- 

 determining factors in plants it may be 

 well to note briefly some of the more con- 

 spicuous facts as to sex differentiation with 

 which the student of reproduction and 

 heredity in plants is confronted. 



In plants at least sex-determining fac- 

 tors are to be sharply distinguished from 

 factors which lead to sexual as contrasted 

 with asexual reproduction. "We must be 

 careful, in discussing the factors which 

 may determine sex, to distinguish two ques- 

 tions : first, as to the causes which lead to 

 the occurrence of sexual cell fusion as con- 



