No. 472] 



POLLEN GRAIN VAIUATION 



281 



gametophyte present may function in photosynthesis. Contin- 

 ued use has prevented in this case the reduction which took place 

 in those species in which the pollen grain enters the micropyle 



In addition to the specific conclusions in regard to Picea (see 

 pp. 270 and 275) the following more general ones are drawn, some 

 of which are suggested rather than demonstrated: — 



1. The variations in the male gametophyte and other structures 

 in the pollen of gymnosperms, indicate that in this group there are 

 examples of progressive reduction of some of those structures. 



2. This reduction is by a gradual modification and not by 

 mutation, and is due to the disuse of the vanishing structures. 



3. The different structures are not necessarily reduced to a 

 corresponding degree in the same species. , 



4. The suppression of the male gametophyte in gymnosperms 

 is a distinct advantage w^here the function of photosynthesis is 

 impossible to it. 



5. The occasional prothallial cell in the pollen of angiosperms 

 indicates that in this group also there was a reduction by gradual 

 modification. 



6. The division of the non-functional male nucleus in the egg 

 of some of the gymnosperms and its fusion with a segmentation 

 nucleus of the fertilized egg in Abies halsamea, strengthens the evi- 

 dence for the view that the endosperm of angiosperms is phyloge- 

 netically a modified gametophyte and not a modified embryo. 



7. The extremes in the variation of the male i^amcropliyte 

 among the genera of gymnosperms are found in Araucaria with a 

 gametophyte of from 20 to 44 cells, (provided my iiitt-rpn-tati.)!! 

 of I.opriori's observation is correct) and Crijptonin-ia japouica 



prothalhuin. but in which even the division wall l)etwetMi the tube 

 nucleus and the primary spermatogenous nucleus is m) tui^itive 

 as almost to escape detection. 



The writer has no intention of makiiiir any further r>tiuati<»ns 



he felt that the opportunity to make the observations here recordeiL 

 though arising only incidentally, ought not to be neglected. 

 Botanical Depaktmknt of the 



