1892.] PUBLIC DOCUMENT — No. 33. 223 



of this station (p. 210), and with most parasitic fungi. The 

 only penetration of the host by this fungus occurs where its 

 creeping vegetative threads send out, from slight lateral 

 projections, short branches which grow downward, piercing 

 the outer walls of the epidermal cells and swelling into club- 

 shaped bodies within the cavities of these cells. By means 

 of these club-shaped organs, the haustoria, the parasite 

 obtains its nourishment by the absorption of the contents of 

 the invaded cells. 



The superficial threads grow and branch freely, and soon 

 begin to send up erect, vertical threads, from which, after 

 they have reached a certain length, spores are formed by the 

 cutting oft' of the tip and of successively lower portions 

 by consecutively formed cell-walls. Each oblong segment 

 becomes, in its turn, rounded off at the angles and somewhat 

 enlarged at the middle, and then falls from its support, ready 

 for germination. On a well-developed thread one may thus 

 see a chain of spores in all stages of development. These 

 spores may vary considerably in size in specimens from the 

 same source ; but they do not usually, if ever, differ so 

 widely as do those from Dr. Fisher's and Professor Bailey's 

 specimens. Between the two there is a considerable differ- 

 ence in form as well as in size, which may point to a specific 

 difference in the parasites from the two sources. The 

 remarks concerning treatment of the disease of cucumbers 

 will apply equally to both forms, whether they represent 

 variations of the same species or not. These spores, when 

 fully ripe, germinate readily in water, but do not develop 

 far. Each gives rise to a germ-tube, usually near one of 

 the original corners of the spore ; but this tube rarely reaches 

 a length greater than twice the short diameter of the spore. 

 On nutrient gelatine, prepared with an infusion cither of 

 prunes or of cucumber leaves, the spores will develop no 

 farther than in water ; but in a drop of water on the surface 

 of a living cucumber leaf they send a branch of the germ- 

 tube downward, as a haustorium, into the underlying 

 epidermal cell, and then grow and branch freely, until a 

 considerable mycelium, forming a spot upon the leaf, is 

 developed. From the readiness with which the leaf and 

 Btem and all succulent parts of the plant are attacked in this 



