383 



(nisi). These medullary rays form the point of departure for tlie fan-like 

 gnarl formations (sp) which, in later development, display a central wood 

 body (kh) and a distant bark layer (r). 



A cross-section through the branch at such a warty place shows (Fig. 

 64) that the wart represents a conical 

 outgrowth (k) of the inner bark, 

 which has ruptured the outer bark- 

 layers, but is still coAered by them, 

 like lips (/). The edges of the lips 

 are dead, and a mycelium is usually 

 fo\md in the depressions. This grows 

 f)ut into the outer, browned and dying 

 or already dead cells of the primary 

 gnarl cone (p). If we trace back the 

 excrescent tissue which, towards its 

 base, possesses a wood layer com- 

 posed of slender, reticulately thicken- 

 ed vascular cells, passing over into 

 the normal wood ring, it is found 

 to be only a simple outgrowth of a medullary ray. 



Fig. 64 illustrates an advanced stage of the medullary ray outgrowth 

 of a branch at the end of the first year (the year of its production) ; the 

 left side still shov.s the normal bark structure; at ak are the suberized 



Ci-oss-seetion throug'h a part 

 twig covered with gnarls. 





Fig. 64. Cross-section througli the bark of the black currant; healthy tissue 

 at the left; at the right a continued outgrowth of the medullary rays. 



remnants of the outermost bark layers shed in the course of the year of its 

 production, which contain scattered crystals of calcium oxalate. These 

 remnants are still connected in places with the discolored, uninjured cork 

 lamellae (gk) which enclose the twig, like a firm, uniform girdle. Below 



