CORMOPHYTASTER AND XENIOPHYTE. 241 



angiosperms as prothallus, at once indicating its equivalence with 

 the structure known by this name in the higher cryptogams and 

 facihtating remembrance of the close parallel between pteridophytes 

 and spermatophytes in their alternation of generations ; and to con- 

 tinue to speak of the angiospermous endosperm as "albumen." 

 But quite apart from the undesirability of perpetuating the latter 

 word except in the most general taxonomic usage, there is a deep- 

 lying morphological reason for giving a special designation to this 

 " endosperm " of the highest plants. 



From the point among thallophytes where an alternation of gen- 

 erations is first recognizable either in somatic or nuclear differentia- 

 tion, that part of a life cycle which produces egg or sperm, or 

 which has the haploid or as Lotsy has called it the x chromosome 

 number, is spoken of as the gametophyte or sexual generation ; and 

 that part which produces neither egg nor sperm but begins with 

 them, and which has the diploid or 2.v chromosome number, is 

 spoken of as the sporophyte or non-sexual generation. To be sure 

 not all cells that are not haploid are diploid, for transient fusions of 

 more than two nuclei are known, and the beginnings of the endo- 

 sperm in a number of aberrant angiosperms start with a blended 

 endosperm nucleus comprising several haploid nuclei ; but it is char- 

 acteristic of the reserve tissue in question that its origin is not in a 

 reduction of chromosomes giving a haploid tissue (as in the game- 

 tophyte), or solely in a fusion of contiguous nuclei giving 2.v (as 

 usually in the sporophyte), or nx chromosomes (as in rare and ex- 

 ceptional tissues and in aberrant angiospermous endosperm), but 

 that it is a structure distinctly not forming a part of either gameto- 

 phyte or sporophyte. Its origin is found in a union involving the 

 2x or exceptionally nx "endosperm-nucleus" (itself derived from 

 a union of the polar nuclei of a typical eight-nucleated embryo-sac, 

 or from the fusion of several nuclei when this number has been 

 increased), and a second nucleus of the pollen as yet indistinguish- 

 able from its sperm companion which unites with the egg to form 

 the embryo or initial of the sporophyte ; and this union differs from 

 fertilization in the usual sense only in that one of the combining 

 nuclei has already fused with one or more others so as to have 

 more than haploid chromosomes. 



