A CABBAGE DISEASE. 



77 



thickened and darker round the ostiole. For a long time these con- 

 tain nothing but imperfect asci filled, except at the summit, with 

 dense protoplasm crammed with oily granules. But later a few will 

 be found in which spores are evidently being formed, and ultimately 

 mature asci, with spores which will readily quit the ascus on the 

 application of pressure, will be discovered. These spores are for a 

 long time simple (as Berkeley and Cooke found them), but at length 

 uniseptate, hyaline, between oblong and cylindrical, obtuse at both 

 ends, but somewhat thicker in the upper than in the lower half, ix. 

 tending to become clavate, and measuring 17-20 X 3-4 /x. The asci 

 are broadly clavate when young, and more or less cylindric-oblong 

 when mature. There are no paraphyses mingled with them, and the 

 spores are usually arranged in a double or even in a treble row. 



The MycospHaerella (which was formerly called Sphaerella) has 



Fig. 24. — MYCOSPHAERELLA BRASsicicoLA, piecc of affected cabbage 

 leaf ; &, the Phyllosticta spores ; c, the ascospores ; d, a mature 

 ascus, \b and c, x 600.] 



been met with in various parts of the country, but seems to be more 

 usually found on old or dead cabbage leaves. The pycnidial stage is 

 a true parasite, attacking the living leaves with great virulence, and 

 by destroying a great part of the chlorophyllose tissue it weakens its 

 victim and renders it useless. A Mycosphaerella much resembhng 

 the present one is common everywhere upon the Broad-leaved Dock, 

 Rumex obtusijolius. This also does its work chiefly in the imperfect 

 stage, but the latter is not pycnidial, as in Mycosphaerella hrassicicola, 

 but conidial, and produces its spores quite superficially on the under 

 side of the leaves. The small pale round spots, surrounded by a 

 purple border, which it causes on the Dock leaves, are familiar, and 

 the fungus in this stage was called Ovularia obliqua, or, still earlier, 

 Peronospora ohliqua. Later the Dock leaves are covered with similar 

 darker, but unbordered, spots, densely dotted over with the little 

 black perithecia of Mycosphaerella Rumicis. It is probable that both 

 these species (and the allied ones which cause spots upon leaves) 

 would be better classed under the genus Stigmatea. 



No suggestion is known of any remedy for this disease ; there 

 are few remedies, if any, that would not cost more to apply than the 

 benefit which would be derived from them could repay. 



