PHYTOLOGY. 



THE OLUB-EOOT PUlT&US.i 



By a. STEPHEN WILSON. 



THERE can, I think, be little doubt that the fungus or 

 vegetable parasite, discovered by M. Woronin, and by 

 him named Plasmodiophora b7'assicce, is the true cause of what 

 is called club-root and finger-and-toe in turnips, cabbage, char- 

 lock, and other cruciferous plants. The great importance of the 

 turnip crop in the husbandry of this country gives the investiga- 

 tion of this fungus an interest of a highly practical and economic 

 character. We are here in the presence of an enemy the strength 

 of which is certainly on the increase ; and which threatens, if no 

 countervailing strategy can be devised, to render the turnip crop 

 as uncertain and precarious as the potato crop has been rendered 

 by another parasitic fungus, the Peroiiospora iiifestans. 



The observations ' of Woronin were made chiefly on the cab- 

 bage, and in reference to the great destruction caused in recent 

 years to the cabbage crop in Russia, and more particularly in the 

 market -gardens around St Petersburg. My own repetition of 

 these observations has hitherto been chiefly confined to the 

 turnip, including only such comparisons with cabbage, charlock, 

 and mustard, as showed that the parasite was the same in all 

 cases. That it is so, however, is an assumption based only on 

 the optical data patent to the microscope. The plasmodic 

 masses ramifying through the cell tissues of the roots have the 

 same appearance in all these plants ; while the ripe spores which 

 form the final stage of the plasmodium, and which are globular 

 in shape and very uniform in size, have also in all cases the 

 same dimensions : thirty- four millions of them can lie upon a 

 square inch. 



It would be impossible to go into the whole subject at present. 

 I shall therefore select one branch. Considerable interest has 



^ Read before the Cryptogamic Society of Scotland, at Forres, Sept. 1879. 



O 



