Feb., 1908.] Polar Conjugation in the Angiosperms. 257 



(Italics not in the original.) The pollentube is so remarkably 

 distinct in Sagittaria and produces such marked changes that I 

 am certain I could not have overlooked it in the stages where 

 polar conjugation takes place, especially since the study of the 

 pollentube was one of the main objects of this investigation. 



Thus it is certain that in some plants the polar nuclei have 

 learned to conjugate without the influence of the second sperm 

 nucleus or even the pollentube. The question now arises as to 

 how the polars acquired this remarkable ability if they do not 

 represent opposite sexes. For it seems excluded that one could 

 think of the Angiosperm female gametophyte as being a direct 

 descendant of an hermaphrodite thallus, the polar nuclei being 

 descendants from male and female gametes. It is altogether 

 probable that the Angiosperms passed through the Heterospo- 

 rous Pteridophyte stage before becoming seed plants. Porsch's 

 view, therefore, seems the correct one, that the triple conjugation 

 results from the essentially female character of the polars. If 

 therefore a conjugation takes place without the presence of the 

 second sperm, this must be looked upon as a special sort of 

 parthenogenetic development. All polar conjugations, accord- 

 nig to this view, had their origin in the original conjugation of 

 one or both polars with the second sperm, typically in the second 

 way through triple fusion. 



Now the question arises as to whether there is a triple fusion 

 in Sagittaria and other such cases. Does the second sperm 

 come down later and fuse with the polars acquired the property 

 or function of conjugating with each other through their common 

 attraction to the second sperm with the first upper endosperm 

 nucleus after the partition wall is formed at the end of the 

 division of the definitive nuclues? This division takes place 

 about the same time as the first division of the oospore, and such 

 a possibility is suggested by the following facts: The second 

 sperm seems to remain in the tube for some time after the first 

 one escapes to unite with the egg; the upper endosperm nucleus, 

 immediately after the division of the definitive nucleus, begins to 

 travel upwards ; the lower endosprem nucleus presents a remark- 

 ably different development from the upper one. But no weight 

 is to be attached to the suggestion until further investigations 

 are made. 



True endosperm, as has been suggested by several investi- 

 gators, may be present even in Gymnosperm archegonia. A 

 true endosperm might originate from the division of a ventral 

 canal cell without conjugation of the second sperm with the 

 ventral canal cell. In Angiosperms an endosperm might result 

 from the conjugation of either polar nucleus with the second 

 sperm; from the conjugation of both polars with the second 

 sperm, which seems to be the usual mode; or through partial 



