182 Darling: Sex in^ dioecious piants 



ments 



in the off- 



spring is determined by the pollen spore and not by the egg. Al- 

 though the conclusions seem hardly warranted from the data, yet 

 they are in harmony with the results obtained by others. 



It is the belief of the Marchals, of Correns, and of Noll, that 

 this separation of the tendencies occurs in the formation of the 

 spores. Although dioeciousness, as the term is usually applied, 

 refers to the gametophyte in the Br>^ophyta and to the sporophyte 



F 



in the Spermatophyta, yet it is very probable that the separation 

 of the two tendencies is fundamentally the same in both groups; 

 for in both groups two kinds of spores are produced in the same 

 sporangium or microsporangium in equal number. 



From the experiments thus far carried on in plants it would 

 seem that possible assistance in the solution of the problem of the 

 determination of sex in dioecious forms may be had in the study 

 of spore formation. Much attention has been given in recent 

 years to the study of the spores in plants and to the germ cells 

 in animals ; so that at present their general morphology is well 

 understood. It may be regarded, at least as a working hypothe- 

 sis, enforced by the classical work of Boveri on the dispermic sea- 

 urchin egg, that each chromosome or group of chromosomes 

 bears a definite relation to the development of particular parts of 

 the organism. With this as a basis, the works of McClung, 

 Stevens, Montgomery, Wilson, and others on the spermatogenesis 

 of insects are particularly significant. It has been found in nearly 

 one hundred species that there are two kinds of spermatozoa pro- 

 duced in equal number, differing in the character of the chromo- 

 some complex. In these cases there are two methods of forma- 

 tion of the chromosomes ; most of them are formed by the seg- 

 mentation of the spireme thread, but the so-called *' accessory" 

 or " idiochromosomes " (Wilson, '09^) arise generally at least 

 from a chromatin nucleolus. The difference in the two kinds of 

 spermatozoa formed is due to the distribution of these idiochro- 

 mosomes. Regarding the determination of sex these facts are ol 

 special interest, since the fertilization of the egg with one kind of 

 spermatozoa always produces a male individual, while fertilization 

 with the other kind produces a female. The natural inference is 

 that it is the idiochromosomes which have to do with the determi- 

 nation of sex. 



