Feb., 1918] Sexual Diniorp/iisni 103 



Physiological states may be due to chemical or other causes. 

 Among the conditions in which organisms may be growing or 

 living, the following may be mentioned : An active or quiescent 

 state; vigorous or exhausted; sterile or fertile; immunity to 

 disease at a certain age or susceptibility; specific diseased con- 

 dition, like cretinism in children, or normal; gametophyte 

 or sporophyte (without change of chromosome number) ; 

 female or male; carpellate or staminate; juvenile state or mature 

 state (like certain Acacias and Junipers) ; water form or air 

 form; root state or stem state (usually with change of environ- 

 ment); conidial stage or sexual; protonema or scaly moss 

 plant; difference of unusual morphological expressions without 

 any hereditary difference, as for example, two or more very 

 different types of insect galls on the leaves of celtis occidentalis 

 L. In the case of the transition from gametophyte to sporo- 

 phyte and vice versa, there is usually a change in the chromo- 

 some number which might be assumed to be the cause of the 

 remarkable change in morphological expression, but there are 

 many examples in both mosses and ferns, and also in the 

 flowering plants, where the change takes place in the vegetative 

 tissues without a shifting of chromosomes. The study of 

 apogamy and apospory should shed much light on the nature 

 of sexual and nonsexual states. 



Before presenting the evidence in hand on the development 

 of dimorphism in the heterosporous sporophytes a few general 

 facts may be given in relation to sex as expressed in the game- 

 tophyte. The term sex used in its strict sense applies both 

 to diploid and haploid individuals; among animals to diploid 

 and among plants more commonly to haploid individuals, 

 although there are numerous algae in which the life cycle is 

 essentially similar to that of the animals. 



As already stated, there is a gradual development from a 

 condition where no difference is apparent between the con- 

 jugating cells except the mutual attraction at a certain period 

 to highly specialized cells, and further through hermaphordite 

 organisms with strikingly different sexual organs on different 

 parts of the same body up to completely unisexual individuals. 

 In the past it has been assumed that sexualit}^ was evolved 

 because of some fundamental utility to the organism, but the 

 doctrine of specific utility as an explanation of origins can have 

 little place in the theory of any investigator who has carefully 



