Maech 8, 1907] 



SCIENCE 



371 



for the sexual than for the non-sexual 

 spores. In many instances the influence of 

 the external factors has been more or less 

 definitely determined and by varying the 

 cultural conditions one may obtain either 

 form of fructification desired. Thus in 

 the hermaphroditic mold, Sporodinia, one 

 obtains exclusively non-sexual spores on a 

 substratum deficient in nutrient but may 

 obtain the zygospores by increasing the 

 concentration of the nutrient. 



Again, the conditions under which the 

 male and those under which the female 

 organs can form do not always coincide. 

 We may illustrate this by the effect of the 

 single factor light. The prothalli of homo- 

 sporous ferns under minimum illumination 

 may be brought to prolonged vegetative 

 growth and thus the formation of both 

 male and female organs be suppressed. 

 When the amount of light is increased to 

 a certain extent only male organs are pro- 

 duced from these sterile prothalli. To ob- 

 tain female organs they must be exposed 

 to a still greater illumination. Such sup- 

 pression of the organs of a single sex on 

 plants normally showing both sexes is not 

 to be confused with sex determination in 

 the offspring of dioecious plants. 



There are a number of facts which are 

 assumed to indicate that in all dioecious 

 plants one sex is dominant and makes its 

 appearance while the other remains latent. 

 Thus a female plant is considered not pure 

 female, but is supposed to contain the male 

 character in a suppressed condition though 

 not capable of being brought to light by 

 simple changes in external conditions. 

 Male and female willow plants are fre- 

 quently found with flowers of the opposite 

 sex, and as has been already explained, an 

 hermaphroditic condition has been pro- 

 duced in Phi/comyces which is normally 

 dioecious. Moreover, by cultivating this 

 hermaphroditic growth by transfers of the 

 vegetative mycelium, it eventually loses its 



hermaphroditic character and in a few 

 mycelial generations is transformed into a 

 male or female growth indistinguishable 

 from one of the sexual races normal to this 

 species. We know too little about what 

 the fundamental differences between male 

 and female actually are to be able to con- 

 jecture in what way this suppression or 

 elimination of one sex is accomplished. 



Especially interesting in this connection 

 is the dioecious plant Lychnis dioica. This 

 wild pink, which has the sexes on separate 

 individuals, is subject to the attacks of a 

 smut fungus which is able to fruit only in 

 the anthers or male organs. If it attacks 

 a male plant it fruits in the male organs 

 already present, coloring them violet. If 

 a female plant is infected which normally 

 never bears male organs, the growth of the 

 parasite in some way stimulates its host 

 to the production of male organs within 

 which it may form its spores. This forms 

 rather a striking example from the plant 

 kingdom of doing good unto those that 

 despitefully use you. Attempts have been 

 made to artificially influence the sex in 

 this plant, but entirely without success. 

 It seems undoubted that in sporophytes of 

 some plants the appearance of one sex can 

 be suppressed in a similar fashion to that 

 so well known for the prothalli of the homo- 

 sporous ferns, but one is hardly warranted 

 in assuming that in no forms the male 

 and female individuals are ever sexually 

 pure. The sex may perhaps be pure in 

 the gametophyte while mixed in the sporo- 

 phyte. 



Some would question the sexual purity 

 even of the gametes themselves. If the 

 gametes contain but a single sex their de- 

 velopment without conjugation in herma- 

 phroditic forms should give rise to uni- 

 sexual individuals — the male gamete to 

 male and the female gamete to female in- 

 dividuals. Some experiments are in prog- 

 ress which it is hoped will throw some light 



