BACTERIA. FUNGI. 



169 



"honey-combed ringworm", and named Favus by doctors; dandruff (Pityriasis 

 versicolor) is produced by Microsporon furfur, and Herpes tonsurans by Tricho- 

 phyton tonsurans. The latter has a remarkable effect on the hair, causing it to fall 

 out and leave the part of the skin affected bald. 



Water-plants are attacked by parasitic fungi comparatively rarely, which is the 

 more noteworthy because such large numbers of non-parasitic epiphytes settle upon 

 the filaments of green algae, and on the brown Fucoidese, and red Floridese. Minute 



Fig. 33 Parasites on Hydrophytes. 

 *, 2 , and s Lagenidium Rabenhorstii. *, Polyphagus Euglence. Rhizidiomyces apophysatu*. 



forms of fungi, invisible to the naked eye, and belonging to the Chytrideae and 

 Saprolegniae, are parasitic upon green algal filaments, especially on the fresh-water 

 species of the genera (Edogonium, Spirogyra, and Mesocarpus. One of these 

 microscopic parasites is represented in fig. 33 * 2 > 3 , and bears the name Lagenidium 

 Rabenhorstii. It develops non-ciliated, spherical swarm-spores, which lay them- 

 selves upon the walls of Spirogyra-cells, perforate them, and insert a club-like 

 process. The protuberance forthwith becomes a tube, which increases rapidly in 

 size in the interior of the cell, ramifying and completely destroying the bands of 

 chlorophyll. The branched tubes of Lagenidium reproduce themselves in two 

 ways at the expense of the host's cells infested by them: they form on the one 

 hand so-called oospores by means of fertilization, and on the other sporangia. The 

 latter process is clearly shown in fig. 33 1>2>3 . In this case, one of the tubular 



