CHYTRIDIINEAE 61 



Urophlyctis. This genus also belongs to the Clado- 

 chytriaceae. U. alfalfae causes the crown-gall of lucerne ; 

 U. leproides, beetroot tumour. 



3. Olpidiaceae. This order and the next have been 

 made for chytridians without mycelium. Olpidians were 

 first discovered by M. Cornu in Saprolegnia-fil&menis. The 

 damage they can cause is often very great, e.g. in the disease 

 of seedling cabbages mentioned below. They are not 

 entirely restricted to plants as hosts : the kindred Sphaerita 

 endogena attacks protozoa, and 0. gregarium develops in 

 the eggs of certain rotifers ; Butler depicts one egg being 

 attacked by four zoospores, and others filled with sporanges 

 and resting spores. 



The zoospores of some members of the order are uniciliate, 

 of others biciliate. After swimming for a time zoospores 

 come to rest as a particle of naked protoplasm, which in 

 some cases exhibits amoeboid movement for a time before 

 it becomes of a rounded shape. 



If situated on a suitable host-cell a penetration-tube is 

 formed and the parasite's plasm passes into that of the 

 host, Fig. 15, G. If they do not find a host quickly they 

 break up. 



Some of the names used for olpidians call for explanation : 

 species that bear the order-name are in the minority. The 

 generic diagnosis states that resting sporangia are smooth 

 and without appendage cell in Olpidium ; this is so in Butler's 

 drawing of 0. gregarium. In Olpidiopsis saprolegniae the 



