Maech 8, 1907] 



SCIENCE 



367 



illustrations chiefly from the forms person- 

 ally familiar to me. The researches of the 

 past few years have demonstrated sexuality 

 in the ascomycetes, the rusts and the yeasts, 

 and some would see sexuality in slime 

 molds and even in certain bacteria and 

 blue-green algje. At present one would 

 hardly dare deny the possibility of sex in 

 any group, however low in the scale of de- 

 velopment. Processes so universally pres- 

 ent among both plants and animals one 

 would expect to have some significance in 

 organic development and in the life of the 

 individual. Yet very little is really known 

 about the fundamental questions of sex. 

 We do not know what constitutes a sexual 

 process; what the real difference between 

 male and female actually is; nor, finally, 

 do we know what advantage, if any, the 

 rather complicated sexual process has over 

 other methods of reproduction. A muster- 

 ing of the facts will enable one to say that 

 apparently nothing is accomplished by sex- 

 uality that can not be equally well accom- 

 plished by purely non-sexual methods of 

 reproduction. 



The theory that the sexual union gives 

 renewed vigor of growth would lead one to 

 expect that forms that multiply exclusively 

 by non-sexual methods would show signs of 

 weakness and eventually die out. In fact, 

 however, non-sexual forms are as vigoro^^s 

 as sexual ones. One could often wish that 

 such were not the case when one finds cul- 

 tures of sexual molds overcome in the 

 struggle for existence by bacteria and non- 

 sexual forms of Penicillium. It seems 

 probable that a considerable number of 

 forms among the flowering plants, of which 

 the ubiquitous dandelion may serve as an 

 example, have dispensed with the sexual 

 method and reproduce parthenogenetieally 

 without signs of loss in vigor. Many ex- 

 amples could be given of higher plants 

 which have been cultivated since historic 



times by non-sexual methods. During the 

 last four years, the male and female races 

 of a number of different species of the 

 molds have been cultivated by means of 

 non-sexual spores in separate test tubes 

 where it is not possible for them to repro- 

 duce sexually. In two species 115 non- 

 sexual generations have been reached with- 

 out apparent change in vegetative or sexual 

 vigor. 



As to the variations which sexual repro- 

 duction is supposed to favor or to cheek by 

 a blending of male and female characters, 

 it can be shown by horticultural records 

 that plants propagated by cuttings or by 

 other non-sexual methods are less likely to 

 vary than those grown from sexually 

 formed seed. Tet distinct varieties do fre- 

 quently arise non-sexually and are to be 

 distinguished in no respect from varieties 

 obtained from seed. 



There is great difference of opinion as 

 to what constitutes a sexual act. Nuclear 

 union apparently takes place previous to 

 formation of so-called apogamous embryos 

 in certain ferns and would seem to take the 

 place of the typical sexual process. If graft 

 hybrids are possible, as seems probable from 

 recent investigation, we have in this asso- 

 ciation of vegetative cells from two differ- 

 ent individuals the blending of characters 

 obtainable through the union of differen- 

 tiated sexual cells. Nuclear fusions have 

 been repeatedly observed in vegetative or- 

 gans of higher plants. Moreover, by treat- 

 ment with certain chemicals fusion nuclei 

 may be obtained which divide with an in- 

 creased number of chromosomes. When 

 brought back to normal conditions the 

 number is reduced to that usual to the 

 plant. The phenomena have nothing to do 

 with reproduction and may, therefore, be 

 considered merely as a sacrilegious juggling 

 on the part of the experimenter with the 

 sacred x and 2a;— the gametophyte and 



