



FUNGOUS BOOT-TUBEKCLES. 69 



Internal Structure. 



A study of the internal structure of the tubercle was made 

 from both longitudinal and transverse sections (f. 1), the 

 smallest tubercle being found to possess the various tissues in 

 common with older ones, only in a more rudimentary form. 

 The tubercle consists of the outer corky layer, the outer and 

 inner cortex and the vascular cylinder. Of these tissues the 

 cortical parenchyma makes up the greater bulk of both small 

 and large tubercles, while the vascular cylinder is quite nar- 

 row, and does not extend far into the young tubercle 



(f. 1). 



made 



cells the outer of which are usually broken. Beneath this is 

 a layer of tissue made up of from four to five layers of oblong 

 thick-walled cells, between which and the vascular cylinder is 

 the narenchvma, composed, under normal conditions, of thin 



walled rounded cells. 



ded 



dodermis. consists of a few xylem strands, a large number 



oem cells and some 





both (f. 1). Many resemblances may be noted to the struc- 

 tures of alder, Elaeagnus and Myrica. 



The fungus confines itself to a zone of tissue two or three 

 layers from the cylinder and from eight to ten layers from 

 the outside of the tubercle, an arrangement strictly adhered 

 to in these tubercles, so that no such irregular structure is 



duced 



makes its home 



from 



fected belt 



the base of the tubercle ; in older tubercles the ii 



widens considerably, often cpntaining ten to twelve layers 



of cells in a transverse section, while the vascular cylinder 



_— M —A ■ 



„ ik _ o „ branch 



division of the tubercle. 



The developmental stages of the fungus and the effect on 

 the host cell are best studied from a longitudinal section 

 where the various stages, from the apex to the base, are 

 easily recognized, and inasmuch as general cell infection 

 occurs at the apex of the tubercle, the most abundant young- 

 est stages are found in this region. Although internal infec- 

 tion is most prominent in this region it is also found to occur 



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