138 STATE POMOLOGICAL SOCIETY. 



is the vast multitude of these little branched tops which gives the Avhite, frosty 

 appearance when viewed with tlie naked eye. Upon the extremities of the 

 ultimate branches the ciitexual spores are borne, singly, but as these branches are 

 very uunierous, as the reader may judge, when d represents a highly magni- 

 lied view of one of the extreme tips as given in c, the number of these spores 

 which is formed upon a single spot must be enormous. At / is represented 

 one of these spores with its granular contents tending to collect in ovoid masses. 

 It is these little spores which are the means of })ropagating tlie disease so 

 rapidly from place to place, and therefore the subject of their germination is 

 imjiortant. 



The ordinary method of germination of spores in fungi and other cryptogams 

 is by a simple i)rolongation of their contents into a tube on one or more sides 

 which finally elongate into threads; but in this species and some of its near 

 relations like the i^otato rot, the process is quite ditfercnt, and is styled germ- 

 ination 1)1/ zoospores. In this case the contents of the spore is divided up into 

 from six to ten oval bodies, which finally rupture the spore wall and then 

 escape, each being provided with two little hair-like processes by wliich tliey are 

 enabled to move about. Their movement lasts from ten to twenty minutes, 

 gradually growing slower, when tlicy finally come to rest, send out a tube and 

 grow much after an ordinary spore. Here, then, we have each spore produc- 

 ing a number of smaller motile bodies, which, after finding a suitable place, 

 germinate, — a very prolific method for the propagation and spread of the 

 disease. 



Under the head of the germination of these asexual spores Dr. Farlow has 

 performed some interesting experiments. lie finds they germinate equally well 

 in the dark as in the light. Those sown in the morning germinate more quick- 

 ly and abundantly than those in the afternoon. •'It was not possible to keep 

 the spores which were formed in the night until the afternoon, as they gener- 

 ally fell from their attachments in the morning and began to germinate. In 

 all cases the germination took place with surprising regularity." At the 

 expiration of an hour and a quarter the contents of the sjoorcs had formed small 

 oval bodies Avhicli before long ruptured the cell wall and made their escape 

 from the mother cell. "They passed out rather slowly, usually one at a time, 

 and paused for a moment in front of the opening where they remained as if not 

 quite free from one another. In a short time each body began to extricate 

 itself from the common mass, move more and more slowly, and finally 

 dart off a full fledged zoospore."' 



At g is represented a sjDore with its contents divided up into zoospores, and Zi 

 one of these motile spores separated and provided with its cilia. 



We see, then, that when a single diseased spot has produced its spores, they 

 germinate in a few hours, and there are a multitude of these moving zoos])ores 

 produced therefrom, which move to a new place on the same or another leaf, 

 and there coming to rest, send their threads into the leaf, and a new seat of 

 destruction is soon established. 



Besides these spores which we have just described as asexual (comdial), and 

 produced simply by the formation and separation of single cells at the extremi- 

 ties of the branched external filaments, there is another kind called sexual 

 (oospores) spores because of their method of formation. They are always 

 formed from the mycelium within the tissue of the grape jilant, and may, there- 

 fore, be styled subterranean in distinction from the others, which arc aerial. 



