436 Mr Gregory, Some observations upon 



In the Phanerogams definite sporophylls, arranged in definite 

 positions, are specialized for the production either of megaspores 

 or of microspores ; and in the megasporangium not only does one 

 mother cell alone divide, but only one of the resulting megaspores 

 is permitted normally to come to maturity. 



In the dioecious Phanerogams under normal conditions the 

 tendency prevails for each individual to form one kind of spore 

 only ; that is, one sex only is present in the active state. The 

 opposite sex is present only in a latent condition, but may be 

 brought into active manifestation by a suitable change in the 

 metabolism of the organism (such as is brought about by the 

 destruction of the anthers of Melandrium (= Lychnis) dioica by 

 Ustilago violacea) 1 . 



Thus sex as it appears in the sporophyte of dioecious plants is 

 so far like a somatic character that the separation of the sexes 

 depends upon a discontinuous variation ; such that each of the 

 varieties is characterized by the production normally of one form 

 of sporophyll only. 



The analogy of the heterotype division in plants with that in 

 animals leads us to homologize the entire gametophyte of the former 

 with the gamete of the latter 2 . There is evidence that in animals 

 the ova in some cases bear the male character only, and that the 

 spermatozoa carry the female character 3 , and it therefore appears 

 probable that the same may be true also of the gametophyte 

 generation in those plants whose sporophytes are dioecious. A 

 segregation of the sex-characters takes place, the sex-character 

 transmitted through any gametophyte to the next sporophyte 

 generation being entirely independent of the particular form of 

 gamete which that gametophyte produces. 



A parallel case of the manifestation in the gametophyte of a 

 character opposite to that which is transmitted through it to 

 the sporophyte of the next generation is afforded by the hybrid 

 Epilobium angustifolium. The common form of this plant, which 

 has grey-green pollen, crossed by its white variety — whose pollen 

 grains are white — yields a hybrid whose pollen grains are all 

 uniformly grey-green (Correns ('00), p. 232, footnote). If that 



1 Giard ('89); Strasburger ('00, b). 



2 In the Thallophyta the reduction division takes place at the formation of the 

 gametes (Farmer and Williams (96)) as in animals. 



3 This occurs in parthenogenetic races; e.g. Rotifers, Daphnidae, Polyphemidae, 

 Artemia, Cypris, Hymenoptera, Aphides, and in facultative parthenogenesis in 

 Liparis and some Insects. In those cases where parthenogenesis is constant it is 

 known that eggs which give rise to males have undergone a reduction division, those 

 which give rise parthenogenetically to females have formed only one polar body. 

 See Weismann and Ischikawa ('88), Blochmann ('88) and Petrunkewitsch ('03). 

 (For discussion of these phenomena, see especially Castle ('03).) The partheno- 

 genetic Chara crinata is possibly a case where the ovum bore the female character, 

 and the male character is now eliminated. 



