388 



UREDINEAE. 



The anatomical changes induced in diseased plants of Ji(nipcrm 

 communifi by G. clavariaeformc were investigated by Woernle 

 under my direction. His results were these: in vigorous branches, 

 increased growth took place in the wood, bast, and rind ; in 

 weakly and poorly-grown branches, the wood increased less in 

 proportion to the bast and rind. The most marked increase 

 took place in the bast, and to an almost equal extent all 

 round the branches. This abnormal growth absorbs so much 



mm 





■4 



'"^)/g 



Fio. 221.— Cross-section of :i tract of 

 parenchyma in a malformed Junijier- 

 twig. (After Woernle.) 





1 



^P^fi 



Z=i(~J 



&m\ 



Fig. 222.— Radial longitudinal section 

 through a zone of parenchyma similar to 

 Fig. 221. (After Woernle.) 



water and plastic material that higher parts of the branch 

 gradually die off, and dormant buds break out on the swelling. 

 Increased growth results in increase in the number of medullary 

 rays, while in tlie tangential section their height is increased 

 from 2-10 cells to 10-20 and more; the wood parenchyma is 

 also more abundant, and together with the rays frequently forms 

 large masses of parenchyma in the wood (Figs. 220-223). The 

 tracheae no longer follow a straight course, and numerous 

 intercellular spaces appear between them ; the tracheal walls 

 fre([iiently become thickened and have an increased number of 



