FERTILIZATION AND FRUIT-FORMATION IN CRYPTOGAMS. 



57 



which subsequently, in some cases, puts out sac-like processes and branches and 

 fashions itself into the likeness of the mother-plant without passing through 

 any intermediate stage; or in others, the tube, which represents the embryo, 

 produces first of all from its protoplasm a number of swarmspores. These roam 

 about for a period and then seek out a convenient spot where they come to rest 

 and develop into new individual plants. The additional production by Perono- 

 sporeae of spores on dendritically-branched hyphae growing out through the 



Fig. 205.— Fertilization, fruit-formation, and spore-formation in the Peronosporese. 



' A bunch of grapes attaclced by the Vine-Mildew. 2 Spores on branched stalks projecting through a stoma of a Vine-leaf. 

 3 Fertilization in Peronospora vilicola. * A single spore. « A single spore the contents of which are dividing into swarm- 

 spores. 6 A single swarraspore. ' natural size; 2x80; *-6x350; 6x380. (*-« after De Bary.) 



stomata of the green host-plants is shown in fig. 205 ^ but an opportunity will 

 occur later on of discussing the details of that process. 



The Siphonaceae exhibit a different mode of fertilization from those processes 

 which involve the preliminary construction of a fertilization-tube and a conjugation- 

 canal respectively. All the Siphonaceae live in water or on damp, periodically 

 submerged earth; they contain chlorophyll and are neither parasites nor sapro- 

 phytes. We may take as a type of this group of plants, which includes forms 

 of great diversity, a species of the genus Vaucheria (see vol. i. figure 25a, a, 

 and text p. 23) and use it also to illustrate the processes about to be considered. 



