400 



UREDINEAE. 



characteristic of G. davariaeforTne. No myceliuiQ occurred in 

 the wood. A comparison of normal bast with that of infected 

 twigs revealed changes similar to those already described for 

 G. davariaeforme. In addition, it is to he noted that the 

 thickened bast-fibres no longer occurred in closed masses, hut 

 were often completely absent in the first year after infection, 

 while in all diseased twigs every intermediate stage exists 

 between thin-walled bast-elements and thick-walled bast-fibres, 

 such as never occur in the normal twigs; in fact, many twigs 

 had thin-walled elements only. 



Fig. 235. — Swelling from 

 a brancli of Junipei"ius 

 Sabina attacked by Gr/mno- 

 sporangium sabinae. Dia- 

 meter at thinnest part 1'7 

 centimetre, at the thickest 

 6 cm. (V. Tubeuf phot.) 



Fig. 236. — Sections of a twig of Savin attacked by G. sahinac.- 

 a, At thickest part of the swelling ; &, 3 cm. under a and normal, 

 lu a is shown one of the hollow telcutospore-cushions ; five 

 cushion-scars ; in the second-year ring are two shaded zones- 

 of wood, chiefly composed of parenchyma. ■ (x 25.) (After 

 Woemle.) 



The sporogenous cushions of G. sabinae are formed in quite- 

 a different manner from those of G. davariaeforme. Beneath 

 each cushion the bast increases very rapidly and forms an out- 

 growth, which is still further enlarged by the addition to its 

 apex of six or seven rows of radially arranged cells, rounder 

 and smaller than the bast-cells of the cushion. The mycelium 

 penetrates between these outer cells, and forms over the whole- 

 cellular outgrowth a pseudoparenchyma from which the sporo- 

 genous tissue arises. 



