FUNGI. 17 



Finally, below all the groups thus far mentioned, is one known 

 as the Peronosporem, to which belong those fungi known as 

 " mildeivs." They are delicate, mold-like fungi, usually growing 

 in and upon the leaves of higher plants, and in some cases 

 producing an actual decay of the tissues attacked, as in the case 

 of the " mildew " or "rot" of potatoes. Many members of the 

 group exhibit a definite sexual method of spore-production, 

 approaching in this particular certain aquatic fungi and algte. 



Doubtless a very natural question has ere this occurred to you. 

 If these fungi and their spores are such minute and delicate 

 organisms, how are they enabled to withstand the cold of winter 

 and the drought of summer? The answer to this question is at 

 the basis of much of our preventive treatment. Those fungi 

 which produce ascospores, in closed receptacles, find such a 

 condition a sufficient protection. If they have attacked leaves or 

 fruit, they fall to the ground with the latter, and the developing 

 spores remain protected by Nature, and by the surrounding refuse, 

 ready to spring into pernicious activity with the approach of 

 warm weather. Again, many fungi, under unfavorable conditions, 

 produce what are known as '•'•resting sjxrres^'" spherical bodies, of 

 comparatively large size and resistant qualities, protected by a 

 dense and impervious outer coat. Such spores may retain their 

 vitality for years, ready to germinate upon any favorable 

 opportunity. Still again, the mycelium of many fungi — for 

 example the '■^black-knot" of plum and cherry trees — is perennial. 

 During the winter it remains dormant within the tissues of 

 the plant attacked and is ready in the spring to produce a 

 fresh crop of spores. Finally, the mycelium of fungi tends, 

 under certain circumstances, to become twisted up into knots, 

 often of large size, called ^^ sclerotia." The exterior hyphse of 

 these knots become very much thickened and indurated, and in 

 this sclerotial condition the mycelium of a fungus may retain its 

 vitality almost indefinitely. 



With all these facts in mind — the great number of fungi at 

 present known to science, the high degree of development which 

 they have attained in respect to organs of reproduction, and the 

 success which has marked their varied adaptations to survival 

 under unfavorable circumstances — we are led to wonder that any 

 of our higher plants are able to resist these minute parasites. 

 Doubtless the damage would be far greater, but for one fact. 

 2 



