1 8 Aecidia and Aecidiospores. 



Hut it is quite possible ithat the time of appearance of the aecidia has 

 something to do with their invigorating power, if such exists. They 

 usually appear in the spring, when the first rush of vegetation commences, 

 and naturally the parasite shares in the* strong growth of the host-plant. 

 The nature of the host will likewise affect the result. It may appear on 

 the leaves of an annual such as Helicmthus annum, which also bears 

 teleutospores, or on those of a deciduous shrub such as barberry, the 

 uredo and teleutospores of which occur on wheat and other grasses. But 

 it is a striking fact that the aecidium is so rare upon a grass that, until 

 the discovery of an aecidium on a species of Danthonia in Victoria, only 

 one instance was known, viz., Puccinia graminella, in which the aecidia 

 and teleutospores occur together, the latter being often very rare, or wanting 

 altogether. 



Repeated Formation of Aecidia. The normal development of heteroe- 

 cious fungi, as well as of autoecious forms, follows a regular cycle, as 

 already shown. In those forms possessing all stages in the life cycle, the 

 sporidiola produce only the aecidia, and the aecidiospores in turn give rise 

 only to uredo and teleutospores, as in Uromyces trifolii (Alb. & Schw.) Wint. 

 But among those autoecious species which produce aecidiospores and teleuto- 

 spores without uredospores, this regular succession of forms may be departed 

 from in some cases, and (the aecidiospores, provided the mycelium is not 

 perennial in the host, may repeatedly produce new aecidia before the 

 teleutospores are reached, as in P. senecionis Lib. 



Spermatia 



h 



Sporidiola 



_ _ Aecidiospores 



Teleutospores 



Aecidiospores 



t This repeated formation of aecidia was principally investigated bv 



.el, who named the aecidia arising directly from the germination of 



primary aecidia," and -those arising from the germination 



of aecidiospores "secondary aecidia;" and it was noticeable that spermo- 



nia were usually absent from the latter. Thus the germinating spori- 



um may produce a mycelium which bears only aecidia; but the aecidio- 



s, instead of giving rise directly to teleutospores, may repeat them- 



everal generations, and then give rise to teleutospores. How- 



x>mplete cvcle the aecidia originate only from sporidiola, while 



and 



