342 



UREDINEAE. 



The two-celled 

 which form lilack 



'J 



teleutospores arise from cushions or sori 

 lines on the haulms and leaves of grasses ; 

 they hibernate on the decayed remains and germinate in spring. 

 Each cell of a germinating teleutospore 

 gives off a four-celled basidium (promy- 

 celium), with four short sterigmata from 

 each of which a basidiospore (sporidium) 

 is abjointed (Fig. 182). The sporidia are 

 carried off the grass-host and germinate at 

 once if they alight on leaves or Howers of 

 Bcrberis or Mahonia (Fig. 183). (Tcrm- 

 tubes are formed which penetrate the outer 

 walls of the host into the epidermal cells. 

 The mycelium which results is a branched 

 septate one, and spreads through the inter- 

 cellular spaces of the leaf. About eight 

 days after infection, little yellow spots make 

 their appearance on the upper surface of 

 the leaf. Embedded in the spots will be 

 found the pycnidia (spermogonia), spherical 

 flask-shaped enclosures developed on a web 

 of hyphae, and with their inner walls clad 

 with short rod-shaped conidiophores (sterig- 

 mata), each of which gives off a tiny coni- 

 dium (spermatium) (Fig. 184). A tuft of 

 periphyses arising from the upper part of 

 the pycnidium wall carries the conidia out 

 of the pycnidia in drops of a honey-like 

 fluid emitting a characteristic odour. In 

 regard to the function of these conidia 

 nothing definite is known. 



The next stage begins with the appear- 

 ance of yellow spots on the lower epidermis 

 of leaves. These indicate the presence of 

 a mycelium from which the aecidia take 

 their origin. The aecidia are at first en- 

 closed in a one-layered peridium under 

 the leaf-epidermis, till by their increasing size they rupture both 

 coverings, and project above the surface as cups containing 

 spores (Fig. 184). The aecidiospores originate in a layer of 



Fia. WL — Puccinki firaiu- 

 inis. Genniniitliig tcloito- 

 spore. The promycelium 

 has formed three sterigmata, 

 from the ends of which 

 sporidia are in . process of 

 abjunctlon. (After Tuhisne.) 



