OYMNOSPERM^E. 



403 



logue of a macrospore, which here is not freed from the 

 parent plant. The endosperm clearly bears the same rela- 

 tion to the embryo sac as the prothallium of Isoetes does to 

 the macrospore ; and the corpuscula are slightly modified 

 archegonia. In some corpuscula the resemblance to arche- 

 gonia is very marked, the germ-cell below being surmounted 

 by a short neck ; Strasburger has even discovered a rudi- 

 mentary axial-cell, thus completing the correspondence of 

 these organs to those of the 

 higher Pteridophytes. 



512. Fertilization is effect- 

 ed by means of the pollen, 

 which comes in contact with 

 the apex of the ovule. It is 

 transported from the male 

 flowers mostly by the wind, 

 which accounts for the im- 

 mense quantity produced. 

 When the ovule has reached the 

 proper stage the micropyle is 

 filled with a fluid, which, dry- 

 ing, carries the adherent pollen J^SSZ*Zt$w 

 grains into contact with the ^.J^pg^^^J; 

 apex of the ovule body, where '^ n ^. le g J 8 j^ f w t .^ e ^ 8 ; l^ 6 . |" 

 they germinate and form pol- two corpuscula shown ailed with pro- 



, , ,-. -. toplasm ; A, the neck cell of one cor- 



len tubes ; the latter penetrate puscuium ; p, two pollen grains ap- 



tlie Soft tissue Of the OVule and mtoVMch'the^have eenttwo e p b oUen 



eventually reach the corpus- tube8 ' '' After FrantL 

 cula (Fig. 299). In those cases where the corpuscula are 

 separated from one another each pollen tube comes in con- 

 tact with only one corpusculum (Figs. 297, B, and 299) ; but 

 when the corpuscula are close together a single pollen tube 

 may come in contact with all of them (Fig. 298, 1 and 2). 

 The union of the protoplasm of the pollen tube with that of 

 the germ-cell appears to take place by diffusion through the 

 wall of the former, as no openings in it have been discovered. 

 After fertilization the protoplasm in the germ-cell becomes 

 more turbid and granular, and soon at the base a transverse 

 partition is formed, cutting off a cell, which is the rudiment 



