CHAPTER V. — COMPARATIVE REVIEW.— UREDINEAE, 



279 



Section LXXX. In the second and much most common case the germ-tube 

 of the aecidiospores does not become a promycelium, but forces its way by 

 acropetal growth through a stoma into the interior of the host, and there developes 

 directly into a mycelium. The mycelium ultimately forms gonidia on distinct 

 hymenia and always by acrogenous abjunction ; and the gonidia, which can germinate 

 either directly or after a period of rest, develope a promycelium with sporidia like 

 that of Endophyllum. The sporidia are usually obliquely ovoid like those of 

 Endophyllum, but in some species are round. The germ-tube of the sporidia when 

 it has penetrated into the host gives rise to a new mycelium producing spermogonia 

 and aecidia. These gonidia which form promycelia have been named tcleutospores 

 (Fig. 124 //, III, Fig. 128 A, and Fig. 129). 



The species which produce aecidiospores and teleutospores are again dis- 

 tinguished into two subordinate groups according to the stages in the course of the 

 development. In some the stages of the development in the order of then- 

 appearance are mycelium, aecidium, teleutospore, promycelium, sporidium, and there 

 are no others. This is the case in G-ymnosporangium, Puccinia section Hemi- 

 puceinia, as for instance in P. Falcariae. 



In other species the mycelium formed from the 

 aecidiospore produces other gonidia besides the teleuto- 

 spores, which are called uredosporcs (Tulasne's stylospores). 

 These too arise by acrogenous abjunction (Fig. 124 III, nr), 

 and as regards the time of their development they may be 

 said to be always the precursors of the associated teleuto- 

 spores. They are formed according to the species either 

 in the same hymenia as the teleutospores, or apart from 

 them in special ones which are simply styled uredo or 

 uredo-layer. Being short-lived they are able to germinate 

 immediately after abscision, and put out a germ-tube 

 (Fig. 128 D) which penetrates through a stoma into the 

 tissue of the host like the aecidiospore, and developes 

 directly into a mycelium. The mycelium forms only new 

 uredospores and teleutospores, and since the process of 



germination, the development of the mycelium, and the formation of the uredo on 

 it are very rapidly performed, the sowing of an uredospore is followed in from 

 six to ten days under favourable circumstances by the ripening of the uredo of 

 the next generation ; thus they are especially effective organs for the dissemination 

 of the species which produce them abundantly. 



To complete our account it must be added that the mycelium which forms 

 aecidia may in exceptional cases subsequently produce gonidia, that is teleutospores 

 with or without uredospores. Sometimes individuals of a species, as in Uromyces 

 appendiculatus, sometimes single species are distinguished from the majority by the 

 regular occurrence of this phenomenon, as Uromyces Behenis, U. Scrophulariae, 

 U. Cestri, and Puccinia Berberidis. It is moreover not unusual for the germ-tubes of 

 sporidia, when they cannot penetrate at once into the host, first to abscise a secondary 

 sporidium at their apex, which has the characters of the original sporidium. 



It has been already said that both kinds of gonidia are produced on hymenia on 



FIG. 127. Endophyllum Sernpervivi, 

 Lev. Germinating spore with the pro- 

 mycelium and a sporidium almost fully 

 formed on the uppermost sterigma. 

 Magn. 200 times. 



