832 



THE FUNGI WHICH CAUSE PLANT DISEASE 



ginning of the binucleate condition marks the origin of the sporo- 

 phyte. 



Biologic specialization ^"i' 1^2.174. 309 much as is found in the Erys- 

 iphales occurs also in the Uredinales. There are many species, each 

 of which is found on a large number of hosts. Upon its numerous 

 hosts the fungus may show no morphological variation, yet at- 



i^fel 



Fig. 247. — Conjugate nu- 

 clear division in cells of 

 P u c c i n i a podophylli. 

 After Christmau. 



Fig. 248. — Diagram- 

 matic representation 

 of fusion of nuclei 

 in the teliospore. Af- 

 ter Delacroix and 

 Maublanc. 



tempts to inoculate from one host to another may uniformly give 

 negative results. It further often occurs that one stage, e. g., 

 the aecia of a species may grow upon only one host while the 

 uredinia or telia may grow upon many different species of hosts; 

 and in such cases that seciospores which have arisen on host X, 

 from infection with spores from host A, are capable of infecting 

 host A and that host only; while seciospores which have arisen 

 on host X, by infection with spores from host B, are capable of 

 infecting host B and only this host; and so on for nurnerous forms. 

 Yet the uredinia and telia of these different races may be mor- 



