FUNGOID PESTS OF CULTIVATED PLANTS. 81 



sometimes in rings and patches, and sometimes scattered over all the 

 green parts. At first the cuticle is shining and unbroken, but at length 

 it is irregularly ruptured, to permit the spores to escape. The base of 

 these pustules consists of a mass of irregular, thick, knotted, mycelium, 

 from which arise club-shaped cells, bearing a chain of globose spores, 

 slightly attached to each other, and forming a kind of necklace, the upper 

 one falling away, and then the next, and so on in succession, as they 

 become matured (12-18 n diam.). 



Each spore or conidium when placed in water or a damp situation 

 undergoes just such a change as we have already described for the conidia 

 of the Rot Moulds (see Introduction, p. 2). From five to eight zoospores 

 are formed in the interior, and escape by rupture of the wall of the 

 conidium. Thus each conidium produces from five to eight active 

 zoospores, which finally serve to disseminate the parasite by infection. 



In the same manner also as in the rot mould does the internal 

 mycelium produce resting spores, which, after a period of rest, probably 

 through the winter, develop numerous active zoospores in the spring. 



In the present species the resting spores are globose (30-50 /j. diam.), 

 externally warted with large obtuse warts, and of a brown colour. 



This pest is distributed throughout Europe, and many parts of Asia, 

 Africa, and America. It may truly be said to be cosmopolitan. 



Sacc. Sijll. vii. 792 ; Mass. PL Dis. 59 ; Smith, Field Crops, 86 ; 

 Cooke, M. F. figs. 198-200; Cooke, Hdbk. No. 1564; " White Bust," 

 Journ. B.H.S. vol. iii. 1848, p. 265, with figs. ; Tubeuf, Dis. 123. 



Cabbage Black Mould. 

 Alternaria Brassicce (Berk.). 



This black mould was first described by Berkeley under the name of 

 Macrosporium Brassicce, and was found by him growing on Cabbage 

 leaves in company with the common Cladosporium herbarium, of which 

 he considered it to be probably a condition. The conidia are clavate, and 

 divided by from five to eleven septa, some of which have longitudinal 

 divisions, and are of an olive colour (60-80 x 15-16 /x). Subsequent 

 examination seems to have shown that the conidia are produced in short 

 chains, attached end to end, as is the case in Alternaria, and hence the 

 change of name. 



It is evidently very rare as a garden pest, although it has also been 

 found in France and Italy. The mould is developed on dry spots of dead 

 tissue ; on Cabbage leaves, and may probably be only a saprophyte, which 

 we have never seen, and probably it has not occurred in Britain again 

 during nearly half a century. 



Tubeuf, Dis. p. 518 ; Cooke, Hdbk. No. 1733 ; Sacc. Syll. iv. 2613. 



Cabbage Rot Mould. 

 Peronospora parasitica (Pers.), PL VI. fig. 30. 



Sometimes found in company with the " white rust," and often 

 independently, on the leaves of many Cruciferous plants. 



We have already introduced this mould in the " Pests of the Flower 

 Garden " (p. 21), where it is far less troublesome and dangerous than here, 



G 



