MISCELLANEOUS CROPS. 141 



bing is undoubtedly due to a fungus belonging to tbe 

 Myxomycetes. On the other band, certain wart-like 

 excrescences are produced on the roots of turnips and 

 cabbages by a small weevil {Ceutorhynchus sulcicoUis) ; 

 but these outgrowths are quite distinct from the true 

 club-root. 



Prevention and Cure. — See under the heading of " The 

 Parasites of Turnips." 



The Mould of Cabbages {Peronosjpora parasitica) 

 belongs to the same genus as the potato-disease fungus, 

 and has a somewhat similar life-history. The mycelium, 

 which is provided with haustoria (suckers), infests the 

 interior of the leaves of cabbages, and produces con- 

 idiophores (bearing conidia), which pass through the 

 stomata on the under surface of the leaves. The patho- 

 logical action of this fungus is to produce putrefactive 

 changes in every part of the leaf which comes in contact 

 with the mycelium. The conidiophores (unlike those of 

 Peronosjpora infestans) have a tendency to twist, and 

 therein agree with another fungus, P. ganglioniformis, 

 described later in this chapter. The conidia of the '' cabbage 

 mould" germinate on various cruciferous plants; and, like 

 P. infestans, this cabbage fungus produces oospores (rest- 

 ing-spores) of a yellow-brown colour, which hibernate for 

 several months. P. parasitica is common in the summer 

 and autumn. 



Prevention.— (1) Destroy all the stumps of previously 

 infested crops. (2) The farmer or market gardener should, 

 as far as possible, destroy shepherd's purse, whitlow grass, 

 pennycress, coral root, hairy bittercress, and many other 

 weeds, for both the oospores and the mycelium of this 

 fungus are to be found on these plants, as well as on cab- 

 bages and turnips. 



