No. 4.] FUNGOUS DISEASES. 87 



access than where they are shut oS by the density of the 

 foliage ; hence, as a rule, parasitic fungi attack more readily 

 plants with a dense leafage or of a low, reclining habit than 

 those of an erect habit and of thinner leafage. This fact is 

 well attested by the comparative freedom from disease of 

 tomato plants, tied upright to stakes and trained to a single 

 stem, over the same plants permitted to grow as they please 

 in dense masses close to the ground. Again, the summer 

 spores have no means for successfully resisting low tempera- 

 tures. Summer is pre-eminently their season, and, though 

 they may occasionally resist the cold of the winter if covered 

 over in leaf heaps or otherwise protected, as a general thing 

 the first hard frosts mean their destruction. The burning; of 

 dead leaves, which might harbor them, has, therefore, more 

 than an £esthetic value. 



It is very evident, then, that there are several very salu- 

 tary checks upon the universal prevalence of fungous dis- 

 eases ; so much so, in fact, that we are led to wonder how it 

 happens that an}^ parasitic fungus requiring a host-plant in 

 active life, and a fair degree of warmth and moisture, is ever 

 able to resist the winter. Let us see how this is effected. 



I have heretofore spoken of the summer spores exclusively, 

 and have perhaps given the impression that they constitute 

 the sole means of fungous reproduction. This, however, is 

 by no means the case. In niEiny if not most of the common 

 parasitic fungi there are formed, by the intertwining and 

 massing together of the vegetative threads, small globular 

 receptacles, varying in size, but usually somewhat smaller 

 than a pin head. The walls of the cells composing these re- 

 ceptacles become hard and black, and within the latter, on 

 the approach of cold weather, are formed numbers of little 

 club-shaped sacs, each one containing a small number of 

 spores. Sometimes these receptacles are completely closed, 

 and they never have more than a minute opening at the top. 

 They form a perfect means of protection from cold and drought 

 for the spores borne within them, and thus the fungus is en- 

 abled to pass successfully through the winter. During that 

 period the leaves, fruit or twigs upon which this form of the 

 fungus is borne, gradually decay, and with the advent of the 

 warm spring rains the contents of the receptacles absorb water 



