234 THE LIFE OF THE PLANT 



flowing into the left, or vice versa. The spherical mass 

 thus produced surrounds itself with a wall, and becomes 

 a spore. When set free this spore is capable of germina- 

 tion, and will give rise to a new organism, a new fila- 

 ment of Spirogyra. ^ 



Here, then, we meet with an extremely simple process 

 of fertilisation : two cells fuse in order to form a new cell 

 which serves the purpose of reproducing the organism. 

 This phenomenon, in a still simpler form, is met with 

 in a microscopic fungus — a mould. This mould con- 

 sists of a thin very much branched tube (fig. 66, left- 

 hand side) in which no transverse partition is to be 

 seen ; which means that the whole organism consists 

 of a single cell. In some parts of this cell short branches 

 appear, stretching towards each other. Whenever 

 they meet, the ends of the branches are separated from 

 the rest of the plant by partitions, and swell. Later 

 on the wall disappears where the ends meet, and the 

 contents fuse, thus forming a single cell — the spore. 



Thus in the simplest spore-bearing plants, as well 

 as in the flowering plants, the phenomenon of fertilisa- 

 tion consists in the fusion of the contents of two cells. 

 This phenomenon is even more obvious in spore- 

 bearing plants, because we can actually observe there 

 the fusion of two cells. In the simplest cases we have 

 described, no difference has been noticed in the aspect 

 of the male and female cells, although a closer study 

 of their structure does reveal a distinction between 

 them ; but in other more complicated spore-bearing 

 plants the male cell differs entirely from the female cell 

 in form as well as in character. While the female is 

 non-motile, the male moves about like a microscopic 

 animal, and penetrates (by its own activity) into the 

 organ containing the female cell. There it fuses with 

 it, dissolving in it, so to speak, and fertilises it.^ 



1 In 1897 such motile cells were found in the poUen-tubes of some seed 

 plants. 



