is i'iiyl<h;i:xy 



are always, or usually, so placed. For instance, in Melarn- 

 psoridium betulinum the fceleuto-sori almosl invariably originate 



directly below the stomatal pore. The cause of this cannot be 

 merely the need of oxygen for respiration, since it has been 

 shown that the intercellular spaces of a leaf are all well supplied 

 in that respect. Fig. 37 is drawn from the lower epidermis of 

 a leaf of Betula alba in which teleuto-sori were just beginning 

 to be produced. The same thing is true of the teleuto-sori of 

 Melampsora Larici-epitea and other Melamp8orae,a,wd apparently 

 even of Phrogmidium. In others of the lower groups, Uredin- 

 opsis, Milesinu, etc., uredo-sori are equally so placed, both 



Fig. 37. Melampsoridium betulinum. a, young sori of teleutospores, 

 viewed through the epidermis, showing how they originate beneath 

 a stoma ; at the lower right-hand is a sorus with only two teleuto- 

 spores, x 300 ; b, three young teleutospores, forming a similar 

 sorus, seated on a common base, x 600. 



primary uredo-sori (which represent a?cidia) and secondary. It 

 can be justifiably inferred that this was the primitive position 

 in which the female gametes and afterwards the other kinds of 

 spore-sori were formed at the beginning: in Puccinia and its 

 allies this position is no longer maintained. 



Since in the Ustilaginales (a comparatively non-progressive, 

 if not degraded, group) there is only one kind of spore besides 

 the basidiospore and the ensuing conidia, and this is produced 

 irregularly and not in definite sori, it may be inferred that the 

 same was true of the primitive Uredinales. This one kind of 

 spore must have been the equivalent of the teleutospore. It is 



