EU-.MYCETES.~(a) ASCOMYCETES 



the leaf by haustoria, which penetrate the outer walls of the epidermal 

 cells, the connection being established immediatciv on the «,'ermin:aio*n 

 of the infecting conidium (Fig. 363). As the sexsoir progresses 

 small dark specks make their appearance, large enough to be seen 

 with the naked eye. These are the fruits, or perithecia. • 

 taining one or more asci. In .damp weather these parasit- .» 



quickly, a fact that has drawn almost superstitious attention to them. 

 A very common example is seen in Podosphaera clandestina, which 

 infests the leaves of the Hawthorn in any warm and wet autumn. 



Fig. 364. 

 Piece of epidermis of Hop, showing mycelium (b) and pcrithccia (a) of the Hop- 

 mildew on its surface. A is a large hair. At (b) the first beginnings of a pfhihcciuiii. 



Magnified. (After Marshall \N'ard.) 



A still simpler one, Sphaeroiheca castagnei, causes a disease on the 

 cultivated Hop, though it may occur also on many other )•' 

 The effect of Mildews on the infected plant is that the diseased ..jv.. - 

 take a pale colour, nourishment being withdrawn from them. But 

 there is no malformation. 



After the Hop-Mildew has establislird itself, ami formed a branched, 

 septate mycelium, certain hyphae grow vertically upwards from the 

 leaf-surface without branching: they segment tr.n 

 short lengths, wliich become detaclied in l)asij)etal sei; 

 easily removed when ripe by a breath of air. They will germinate 

 on a moist leaf, and cause new inferlions ilurini: the sum- - 

 (Fig. 363). But later the fruit-bodies {periUiccia) appear, which prv . 

 for the winter's rest (Fig. 364). They arise where the branched 



