1920] WILSON— CROWN-GALL 53 



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occupying irregular cavities in the tissues of the gall (fig. 8). If 

 the spores are not scattered in sectioning they completely fill the 

 cavities. They average 40 fi in diameter. When shaken from the 

 cavities they appear as a glistening brown powder. 



With rare exceptions the spores are spherical in form, except 

 for the depression on one side (fig. 8). Great irregularities of 

 form may occur, especially near the borders of masses of spores, 



with 



formation 



may 





the outlines of the host cell occupied (fig. 11). A group of slitlike 

 pores in the depressed surface is normally a prominent feature of 

 the spores (fig. 9). Bally (3) observed similar pores in the walls 

 of the spores of Urophlyctis Rubsaameni. The walls of the 

 spores consist of two layers, the outer much heavier than 

 the inner (fig. 6). The outer layer is yellow-brown, glassy in 



in sectioning. It is very 



this 



of the Chytridiaceae. A positive reaction with phloroglucin indi- 

 cates that it is lignified, but it does not stain with safranin. The 

 inner layer of the wall is thin and hyaline in appearance; it responds 

 to the zinc chloriodide test for cellulose. In this respect it is 

 like the wall of the sporange of Olpidium Viciae described by 

 Kusano (17). It lacks the rigidity and brittleness of the outer 

 layer. Ridges in the inner layer are of frequent occurrence (tig. 13). 

 In the resting condition the protoplasm of the unstained spore 

 appears to be granular in nature and somewhat vacuolate (fig. 10). 

 The nuclei cannot be distinguished without staining. Flem- 

 ming's triple stain or Heidenhain's iron-alum-haematoxylin may 

 be employed to bring out the nuclei. Many small nuclei are 

 found to be scattered quite regularly through the cytoplasm of 

 the spores (fig. 15). It is difficult to detect the structure of the 

 nuclei at this stage; it becomes easier as the spore develops into 

 a sporange. There is considerable variation in the response of 

 the nuclei to stains. This is probably related to the difficulty in 

 obtaining very thin sections through the spores. Nuclei which 

 have been sectioned show that the chromatin is usually at the 

 periphery, often concentrated at one side. In some preparations 



