FUNGOUS ROOT-TUBERCLES. 75 



dividual tubercles to much branched structures, the largest 

 of which was 3-5 cm. in diameter. The larger clusters are 

 very compact and usually attached very close to a large root 

 (pi. 7). An unbranched individual tubercle may be de- 

 scribed as a cylindrical structure, 8 to 1 mm. in diameter and 

 about 5 to 6 mm. in length, terminating in a smooth rounded 

 tip having no indication of a root cap. Very loose clusters, 



may 



After a 



tubercle has attained a certain length, branching takes place 

 in the tip which may continue until ultimately 24 to 30 



to a single individual. 



may 



dark gray, becom 



much 



tubercles 



almost black, with a grayish colored tip. This dark color 



some 



peels off, thus giving the rough appearance. ^ Individual 



tuwvxv^o v * «~. P . — r sublimate 



and Fleming's weaker and medium solutions. Specimens 

 fixed in corrosive sublimate solutions gave the best results; 

 the osmic acid solution so hardened the material that sec- 



difficult. From the imbedded material 



made 



were stained with Fleming's triple and Heidenhain's iron 

 haematoxylin, but the triple stain set forth clearly all cyto- 

 plasmic and nuclear structures of both the host and fungal 



cells. 



morphological structure of the tubercle is best 



from a median longitudinal section in which the various tis- 

 sues are shown as well as the different stages of development 

 which the fungus passes through in its limited life cycle. All 

 the tubercles retain to some extent the typical tissue systems 

 of a normal root, the cortical parenchyma being greatly en- 

 larged from the hypertrophy which is primarily brought 

 about by the fungus which lives in the cells. The chief tissues 

 of the tubercle are the inner and outer cortex and the vascu- 

 lar cylinder, which is bounded by a thick walled endodermis 

 (f. 14). The outer cortex consists of oblong cells, the walls 

 of which stain a deeper color with gentian violet, while the 



