A Study of Meadow-Crop Diseases in New York 93 



Per cent 



90 

 80 



70 

 60 



50 



O < > 1 -^q I 



Temperature 9 



18' 



27' 



<36* 



Figure 21. effect of temperature on germination of uredjniospores of puccinia 



phlei-pratensis 

 Eighteen hours allows as good germination at 3° as at 26° C. 



had a curve been plotted of the germination in each chamber when the 

 maximum germination was attained in the best one, a more exact idea of 

 the effect of temperature could be obtained. It is significant, nevertheless, 

 that complete germination occurred even at 3° C. within eighteen hours. 

 Apparently 33° C. is too high for the best germination. 



Evans (1907:446-448) studied the disease cytologically and found that 

 a fine, delicate germ tube runs along the leaf surface and swells into a thin 

 appressorium at a stoma. The protoplasm then passes into the substoma- 

 tal vesicle and the appressorium dries up. 



Evans (1907:447) says also that the substomatal vesicle " gives rise at 

 one end to one infecting hypha only, from which the others subsequently 

 arise." The first septum is formed about the third day when a haustorium 

 begins to develop from the swollen hyphal tip as a little tube which pene- 

 trates the cell wall and expands within the cell itself. As the body of the 

 haustorium increases in size, the proximal swollen portion becomes empty 

 and the nuclei pass into the distal end. Sori appear within eight to twelve 

 days. 



Urediniospores produced in the primary cycles initiate the secondary 

 cycles which follow each other at approximately fortnightly intervals. 

 Teliospores may or may not develop later in the season (Eriksson and 

 Henning, 1894:140). 



