4 Robinson, Puccinia viahaceamm and its host plant. 



complete ring of vascular tissue the mycelium only rarely 

 reaches the pith. As in the petiole, there is a definite 

 attack on the starch sheath, medullary rays, and the 

 phloem elements of the vascular bundle. 



On the stem or petiole several pustules are often 

 found in close proximity. Whilst many of these may 

 represent separate infections, some are subsidiary sori 

 that have originated as off-shoots from the main sorus. 

 Text-jig. 3 represents a longitudinal section through a 



sf.sh. 



Text-fig. 2. T.S. part of the stem of Althaea, showing very 

 young pustule and indicating the distrilmtion of the 

 fungus in relation to the tissues. Description in 

 text. X 36. 



portion of a petiole with a maturing sorus {s^ and two 

 younger subsidiary sori (j-^, s.^ borne on the same mycelial 

 system. 



On the leaf blade the sori occur most frequently on 

 the lower side, that is, with the teleutospores directed 

 downwards. Text-fig. 4A, which is a portion of the leaf 

 blade seen in surface view, shows that each sorus is related 

 to several of the finer veins of the leaf. Stomata occur 



