430 FUNGOUS DISEASES OF PLANTS 



The aecidial or caeomal stage may cover practically the whole of 

 the lower surfaces of the leaves. This stage is the one of great im- 

 portance from the standpoint of the propagation or dissemination 

 of this fungus. In the formation of the spores extensive mycelial 

 cushions are developed near the lower surface of the leaf, and from 

 these cushions there arise cells perpendicular to the surface, which 

 elongate, and in time originate chains of the secidiospores. The 

 development of these spores effects a rupture of the epidermis, so 

 that the mature spores are exposed (Fig. 209). The maturity of the 

 spore involves the development of a considerable amount of color- 

 ing matter in the protoplasm, so that when the spores are exposed, 

 the under surface of the leaf is bright orange. The spores are 

 ordinarily ovoidal or more or less globose, sharply vermcose, and 

 measure 12-24 x 18—32^. Germination may take place immedi- 

 ately upon maturity of the spores, and the Rubus hosts may be 

 promptly infected. The lack of a true peridium in this stage is the 

 chief reason for separating the species generically from species of 

 Puccinia. 



The teleutosporic form of this species is of the Puccinia type. 

 Prior to the experiments of Tranzschel and Clinton, working inde- 

 pendently, it bore the name Puccinia Peckiana. The teleutosporic 

 form is relatively far less abundant than the other stages. The chief 

 peculiarity is found in the location of the germ pore in the basal 

 cell, which is always considerably below the dividing wall. 



XXIV. RUST OF ROSES 



Phragmidium subcorticium (Schrank) Wint 



Bandi, W. Beitrage zur Biologie der Uredineen (Teil I). Hedwigia 42 : 

 1 18-136. 1903. 



The various species of Phragmidium are parasitic upon different 

 rosaceous hosts. No species of these rusts produces any very 

 serious disease of a cultivated variety ; nevertheless, consideration 

 should be given to a general study of one member of this genus. 

 The fungus above indicated occurs commonly in moist regions 

 upon several wild roses. Spermogonia and secidia (caeoma type) 

 are produced on the stems, petioles, leaf veins, etc., as orange- 

 red pustules, sometimes inclosed by paraphyses. The spores are 



