VIII] 



UREDINALES 



207 



Fig. 183. Coleosporium Son- 

 chi ; uredosorus, x 545 ; 

 after Holden and Harper. 



group of basal cells of indefinite extent, from which the aecidiospore mother- 

 cells are cut off The aecidium is, in fact, no more a definite organ than the 

 uredo- or teleutosorus, and only appears so in the 

 more elaborate forms because of the modification of 

 its peripheral cells to form a pseudoperidium. The 

 important distinction lies not in the general morpho- 

 logy of the sorus, but in the fact that an association 

 of two nuclei from different cells takes place in the 

 basal cell of the aecidium and in the specialization 

 indicated by the separation of the sterile cells. 



In its general structure the spermogonium, con- 

 sisting as it does of a series of spermatial hyphae 

 with or without circumjacent paraphyses, is not very 

 different from the other sori, and, in the simplest 

 cases, it also is of indefinite extent. 



Omission of Spore Forms. In many rusts one 

 or more spore forms are omitted; the case where the 

 so-called primary uredospore is substituted for the typical aecidiospore has 

 been already described; these and others in which the characteristic aecidium 

 or caeoma alone is lacking are distinguished by the prefix brachy. 



Hemi- indicates the presence of uredo- and teleutospores without aecidia 

 or spermogonia. 



The suffix opsis is used for forms with aecidia and teleutosori. They 

 lack uredosori but a few uredospores are sometimes found in the teleutosorus. 



Micro- and lepto- forms have teleutospores with a few occasional 

 uredospores and sometimes spermogonia. The teleutospores germinate in 

 the former group only after a period of rest, in the latter upon the same 

 host plant as soon as they reach maturity. 



Species with the full complement of spores are distinguished by the 

 prefix eu. 



As already pointed out, the sporophyte in some of the brachy- species 

 starts from the fertile cells at the base of the so-called uredosorus, and this 

 may very probably prove to be true in all cases where the ordinary aecidium 

 is absent and spores developed like uredospores accompany the spermogonia. 



The alternation of generations in the -opsis forms is also normal, for 

 these are characterized by the omission of typical uredosori the development 

 of which is related to no significant change in the nuclear life-history. 



In micro- and lepto- forms the basidiospore germinates to produce, as in 

 eu- species, a mycelium of uninucleate cells on which spermogonia may 

 occasionally be borne. The mycelium becomes binucleate either during 

 vegetative development {Uromyces Scillariim, Puccinia Adoxae) or below 

 the young teleutosorus, and the fusion in the teleutospore takes place in 



