FUNGOID PESTS OF CULTIVATED PLANTS. 83 



large and rather rounded or irregular bleached spots, upon which the 

 perithecia, or receptacles, are scattered, but larger in size generally. The 

 fructification is more complex, since, instead of naked sporules, the recep- 

 tacles enclose long transparent vesicles called asci, each one of which 

 contains eight sporidia. In this species the sporidia are oblong, and 

 divided in the centre into two cells (18 x 4 /*). 



The mature stage of this pest, in the form of Sphcerella, is not reached 

 until the leaves have lain some time on the ground. 



This condition of spot has also been found in France, Belgium, Ger- 

 many, and Italy, but is nowhere very common. 



It is scarcely likely to give more trouble than to pick off and burn the 

 diseased leaves of the Phyllosticta form, as they appear. 



tiacc. Syll i. 1989. 



CLUB BOOT. 

 Plasmodiophora Brassica (Wor.), PI. IX. fig. 101. 



Club Eoot is so well known, not only in Turnips but in Cabbages and 

 other plants of the family, that no detailed description is necessary. 



It is now admitted that the disease is caused by a kind of slime fungus, 

 which occupies the club. It commences early in the growth of the plant 

 affected. The rootlets are swollen in a spindle-shaped manner, usually 

 with a smooth surface, and the plant presents a sickly appearance. At 

 first the cells of the clubbed roots are filled with a yellowish slimy sub- 

 stance which is the early condition of the fungus. Later on this sub- 

 stance will be seen to have undergone a change into myriads of minute 

 spherical spores. During winter these spores remain quiet, but in spring 

 they ripen and prepare for germination. This is done by the gradual 

 conversion of each spore into an active motile zoospore, and each atom, 

 being free, is capable of moving as it pleases by aid of its whip-like tail 

 in any film of moisture. 



When the motion ceases, these bodies coalesce into a small slimy mass, 

 which in turn coalesces with other masses until a large mass is formed. 

 These viscid masses are washed out of the tissues by early rains, and 

 move about in the moisture by pushing out little portions of their sub- 

 stance like legs. In this manner they come into contact with the roots 

 of seedling plants, and the disease is communicated. 



The application of quicklime destroys the germs in the soil. Thirty- 

 five bushels per acre is enough to arrest the disease. 



Sacc. Syll. vii. 1568 ; Smith, Field Crops, p. 94, figs. 34-39 ; Ward, 

 Dis. PL p. 47 ; Mass. PL Dis. p. 334 ; Journ. B.H.S. xxvi. 1901, p. 190, 

 xxvi. 1902, p. ccxix ; xxviii. 1904, p. 636 ; Tubeuf, Dis. p. 524. 



BLACK ROT OF CABBAGE. 



Pseudomonas campestris (Sm.). 



This disease, long known in America, has now appeared in Britain. 

 It may appear on the plant at any period of growth. Dwarfing, or one- 

 sided growth of the heads, or absence of head is a symptom. If the 

 stumps of affected plants are broken, a dark ring will be seen, correspond- 

 ing to the woody part of the stem ; in bad cases this blackening may be 



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