394 



UREDINEAE. 



marked swelling on one side only (Tig. 227). In the needle- 

 form the swelling results from increased growth of the rind, 

 with a simultaneous decrease of growth of the wood ; in the 

 twig-form the growth of both wood and rind is much increased. 

 With the twig-inhabiting form the medullary rays and wood- 

 parenchyma increase, and at the same time become filled with 

 mycelium (Fig. 228); whereas with the other form the medullary 

 rays are at most only somewhat broader, and no mycelium can 

 be found in the wood. The greatly swollen rind in the case 



FICJ. 227. Section of a nine-year twig 

 of Juniper attacked by Gymnosporangiv. m. 

 The rind under the spore-cushion is 

 much thickened ; the wood towards the 

 same side is much broken up by tracts 

 of parenchyma. (After Woernle.) 



FIG. 228. Tangential section through diseased 

 wood beneath a spore-cushion. The wood- 

 elements are much displaced by abnormal tracts 

 of parenchyma. (Only one of the latter has been 

 filled in, the others left blank.) (After Woernle.) 



of the twig-inhabiting form is due more to increased growth 

 of the cortical cells than to increase of bast-parenchyma; in 

 the needle- form, however, the swelling is the result of increase 

 of the bast, especially of the bast-parenchyma. In twigs 

 infected by the needle-form, the mycelium may be found all 

 round, but it has difficulty in making its way radially to the 

 cambium; in the twig-form the mycelium, as early as the 

 spring following infection, will be found to be in close contact 

 with the cambium on the infected side, although it requires 

 several years to pass round to the cambium on the opposite 

 side of the twig. The mycelium and spores of the two forms 

 differ little from each other." 



