12 Robinson, Piiccz?na vialvaceartivi mid its host plant 



time onwards there is no great extension of the area 

 of the host tissues invaded by the fungus, the further 

 vegetative phase consisting in the increase in amount of 

 the mycelium in the region already occupied. 



The reproductive phase begins with the growth of 

 fertile branches radially outwards from the mycelium 

 massed in the collenchyma. These insinuate themselves 

 in rows between the walls of the outer layers of collen- 

 chyma and ultimately give rise to the teleutospores, which 

 are thus generally developed between the collenchyma 

 and the assimilating tissue {Text-fig. 2). Finally the 

 increase in size of the cells of the cortical parenchyma and 

 of the collenchyma, together with the great accumulation 

 of mycelium and the growth of the developing teleuto- 

 spores, brings about the crushing and ultimate rupture of 

 the assimilating tissue and the epidermis. 



It is well known that the sori on the leaf often drop 

 out after maturity leaving circular holes, and that those 

 on the stem fall away leaving elliptical wounds.'' These 

 are indications that the final fate of the invaded tissues is 

 death, and that the whole cf the affected area is necrosed, 

 none of the mycelium remaining alive in the tissues of 

 the plant. During the earlier stages of the attack, how- 

 ever, it will be shown below that the affected cells remain 

 alive. 



Some confusion seems to e.xist in regard to the 

 haustoria of Piiccinia malvaceaj-inii. While, as mentioned 

 above, Taubenhaus" has recently stated that haustoria are 

 rarely found in this species, they have been described and 

 figured by Kellerman^ and Eriksson.® The descriptions 



^ Plowright, C. H., "A Monograph of the British Uredineae and 

 Ustilaginete. " 



* Loc. cit. 



'' Loc. cit. 



^ " Der Malvenrost." Kitugl. Svenska. Vetensk. Haud., Bci. 47, No. 2. 

 1911. 



