CHAPTER VII— PHENOMENA OF VEGETATION. — LICHENS. 395 



The Chytridieae of the genera Rozella and Woronina, which were discovered 

 by Cornu and more thoroughly examined by A. Fischer l , are parasites on the stout 

 tubes of the Saprolegnieae which are destined to form spores (see Figs. 68 and 69). 

 Rozella septigena, Cornu lives on species of Saprolegnia. Its swarm-spores are 

 ellipsoidal in shape and 6-8 /* in length, and bore their way into the growing tubes 

 of Saprolegnia. When a spore has effected an entrance in this way, it remains 

 visible for a short time in the protoplasm of the tube and then can no longer be 

 distinguished ; it seems to lose its individuality, to distribute itself and be lost in 

 the protoplasm of the tube. The tube at once swells out as a large quantity 

 of fresh protoplasm streams into it, and it divides by transverse walls formed 

 for the most part in basipetal succession into swollen cylindrical or barrel-shaped 

 segments, which are from two to several times longer than broad (Fig. 166). The 

 transverse walls are formed in the same way as in the delimitation of sporangia 

 in Saprolegnia. Then the protoplasm in each segment becomes invested with 

 another special membrane lying in close contact with the first and thus the cell 

 becomes the sporangium of a Chytridium (see section XLVI). About 60-80 hours 

 elapse between the entry of the spore and the emptying of the sporangium. The 

 process is the same if more than 1 spore has entered the tube of the Saprolegnia ; 

 when a single spore entered 2-14 sporangia were observed to be formed, 21 

 sporangia when 4 spores entered the tube. Rozella appears to form resting-spores 

 when many of its swarm-cells have made their way into the Saprolegnia. In this 

 case also the swarm-cells entirely disappear in the protoplasm of the host, which 

 then puts out stalked spherical branches resembling the oogonia of Saprolegnia, and 

 a resting-spore is formed from the protoplasm of each branch (Fig. 166, s). The 

 phenomena observed in Woronina are quite similar to those in Rozella apart from 

 certain differences in the form of the parts. 



If no later investigations bring to light facts at variance with those here given, 

 and this according to Fischer's statements is not probable but cannot however be 

 considered to be impossible, the above case is an instance of a parasite surrendering 

 its individuality, so far as that can be recognised morphologically, after its entrance 

 into the host ; it becomes changed into a part of its host, and the two can no longer 

 be distinguished from one another by our present means of investigation. The 

 parasite also communicates new properties to the host which is some two hundred 

 times its size, and through them the host developes into its own parasite. This 

 transmutation of the host by the parasitic spore which has coalesced with it, though 

 peculiar, is yet analogous with the fertilising effect of the spermatozoid on the 

 oosphere of organisms which in the sexual sense are highly differentiated from one 

 another. 



Fungi which form Lichens. 



Section CXIV. A large number of species of parasitic Fungi employ Algae 

 as their hosts, either unicellular Algae which live isolated, or pericellular Algae, 

 or Algae which unite together in gelatinous colonies. The germ-tube of the Fungus 



1 Ueber d. Parasiten d. Saprolegnieen. Sec also citations on page 171. 



