IN THE VEGETABLE KINGDOM. 59 



authors, however, assert the existence of free cells in this 

 situation, at least in certain families, as the Cupressineae.* 

 Hofmeister in particular mentions the formation of cells in 

 the dilated extremity of the pollen tube, by a process of en- 

 dogenous multiplication. The last formed cells contain 

 granules, along with minute vesicles, which may be the ulti- 

 mate stage of the granules, and fusiform particles, which 

 are perhaps originally the nuclei of the vesicles, and which 

 somewhat resemble the spermatia of Lichens and Fungi.*)" 



The Pollen-tube, after insinuating itself into the tissue 

 of the nucleus, has its growth arrested in some species 

 for a whole season, and only recommences its progress when 

 the " Corpuscula" are fully matured. It then penetrates 

 through the overlying stratum of the nucleus, and through 

 the wall and upper stratum of the albuminous body. Im- 

 pinging finally on the summit of one of the Corpuscula, it 

 displaces the rosette of cells here situated, and either sends 

 down a process into the Corpusculum by invaginating its 

 wall, or becomes merely flattened out over its summit, no 

 aperture being formed either in the wall of the cavity or in 

 that of the pollen tube. After this the germ cell at the 

 base of the Corpusculum resolves itself, by a process of di- 

 vision and sub-division, into a group of eight cells, the four 

 lower being the rudimentary embryos of which, however, 

 all but one abort while the four upper become elongated, 

 by a continuance of the sub-division, into so many cellular 

 iilaments or suspensors, whose growth pushes down the 

 embryos as in the spore of the Rhizocarps into the un- 

 derlying stratum of the nucleus. 



This development in the ovule, the whole of which takes 

 place while it is still attached to the tree, occupies a very 

 long time, many Coniferse not ripening their seeds till the 

 next year after flowering. The fall of the seed arrests the 



* Micrographic Dictionary, p. 518. 

 f Annals of Nat. History, 2d Ser., XIV., 427. 



