HEPEODUCTION OF GYMN0SPER3IIA. 



773 



vegetable kingdom the ovules by the action of the pollen are de- 

 veloped into perfect seeds whilst connected with their parent, the 

 distinguishing character of a seed being the presence of a rudi- 

 mentary plant called the embryo. The modes in which repro- 

 duction takes place, and the after development of the embryo, 

 differ in several important particulars in Grymnospermous and 

 Angiospermous plants ; hence it is necessary to describe them 



1. Eeproduction of Gymnospermia. — We have already given a 

 general description of the pollen and ovules, but as these struc- 

 tures present certain diiFerences in theG-ymnospermia from those 

 found in the Angiospermia, it will be necessary for us to allude 

 to such peculiarities before describing the actual process of re- 

 production. 



The pollen of the Angiospermous division of the Phanerogamia 

 generally consists, as we have seen (pp. 254: — 257), of a cell 

 containing a matter called the fovilla, and having a wall which 

 is usually composed of two coats, the outer being termed 

 the extine, which possesses one or more pores {fig. 556) or 

 slits {figs. 554 and 555), or both ; and the inner, called the in- 

 tine, which is destitute of any pores or slits, and consequently 

 forms a completely closed membrane. Each pollen-grain of the 

 Angiospermia is thus seen to be a simple cell. In the Gymno- 

 spermia, on the contrary, the pollen-grains are not simple cells, 

 but they contain other small cells, which adhere to the inside of 



Fig. 1117. 



Fig. 1118. 



Fig. 1117. Vertical section of the young unirnpregnated ovule of a species 

 of Pinus. a. Nucleus containing a small primary embryo-sac, b. m, 



Micropyle, which is here very large. Fig. 1118. Vertical section of an 



older ovule of a species of Pimis. a. Enlarged primary embryo-sac. b. 

 Endospermal cells within the embryo-sac. c. Pollen-tubes penetrating 

 the apex of the nucleus. 



the internal membrane close to the point where the external 

 membrane presents a slit. 



The ovules of the G-ymnospermia, excluding those of the G-ne- 

 taceae which require further investigation, consist of a nucleus 



