84 MISSOURI BOTANICAL GARDEN. 



deeply 



of the 



mal 



from that of 



oem 



arranged alternately and radially, with a few pith cells in the 

 center. The phloem, however, makes up the greater bulk 

 of the tissue. 



In the young tubercles the vascular cylinder does not ex- 

 tend far into the apex, whereas in older ones the cylinder 

 with some cortical cells surrounding it, grows out into a 



■ 



off. These, no doubt, have 

 to that of the ordinary root. 



branches 



some absorbt 



mav best 



median 



found 



be traced 



base of the tubercle. The infecting region 



tubercle, 



embryonic or comparatively young cells afford the proper 

 conditions for the fungus. There are numberless cells ad- 

 joining, but none of them show indications of being affected. 

 This layer is shown in f. 29. The entire infected region 

 has the shape of a cylinder, ranging from one to two cell 

 layers in thickness, and tapers slightly toward the apex of 

 the tubercle where it always remains open. This region 

 nay be recognized from the place where the tubercle begins 



i arrangement seems to be indicative of the 

 gus has certain selective properties in de- 



i 



to taper. 



may best 



An- 



other strange feature is the fact that it will live in one or 

 two layers of cells, growing neither farther out nor in. Prob- 

 ably the cells have acquired some immunity after having 

 attained a certain age, or the infected region may bear some 

 relation to the central cylinder and also to the air outside 



may 



most appropriate position. 



The young uninfected embryonic cells arc usually filled 

 with starch grains imbedded in a spongy cytoplasm in which 



frequently a large vacuole is present. The starch grains are 



