THE FLOWER 



233 



development of the embryo, and the transformation of 

 the ovule into the seed ; its influence also extends to 

 the carpel, which grows after fertilisation and develops 

 into the fruit. 



Such in very general outline is the formal morpho- 

 logical aspect — the only one known to us — of this 

 phenomenon of fertilisation. Let us now observe how 

 the same process takes place at the other pole of the 

 vegetable kingdom, among the simplest plants, like the 

 weeds and the moulds. 



Fig. 66. 



Here is a microscopic weed, Spirogyra, which we have 

 already studied, with its characteristic spiral bands of 

 chlorophyll (fig. 66, right-hand side). At a certain 

 stage of development the filaments, of which the 

 organism consists, become parallel to each other, as is 

 shown in the plate. In some cells the contents gather 

 into lumps, round or oblong in shape. Meanwhile the 

 walls of two adjacent cells form swellings, which grow 

 towards each other and meet ; the partition dividing 

 them is absorbed and vanishes, and the contents of 

 the two cells fuse, the contents of the right-hand cell 



