spike; ;;/, pith; h, wood; r, l^ark ; c, cambium; uist, medullary rays of the 

 mother branch ; hm, wood layer; rm, bark layer of the spike; n, meristematic 

 cap of the si)ike; hm' , rm' , wood and bark of the lateral sprouts of the 

 gnarl cone; h' . second annual ring; h" , third annual ring. 



b'ig. ()i is a highly magnified longitudinal section thro\igh a si)ike of a 

 gnarl lying within the bark of the mother branch. Fh, indicates the phel- 

 logen : k, tlie cork layer ; Fc\ tlie collenchymatically thickened cells ; Pr, the 

 I)arcncliynia of the ])rimary bark of the mother branch, of which the inner- 

 most layers begin to be tilled with starch; St, 

 starch ; .\hp, dead layer of parenchyma cells of 

 the primary branch bark; M, meristematic tip of 

 tlu- spike; ./, cells of the wood layer of the gnarl 

 cone with their pores d'ar); c, cambium; B, 

 bark of the spike. 



Therefore, the cone mantel (Abp), composed 

 of the shaded cells, forms the boundary between 

 the spike primordia and the mother bark of the 

 twig and may be clearly recognized as the axial 

 cylinder, since the wood layer (A) is covered 

 v\ ith its own bark tissue ( B) while, between both, 

 tlie cambial zone (c) becomes recognizable. The 

 wood r}lin(ler is composed chiefly of very porous 

 ]iai-enchymalous wood (For). The bark tissue 

 abounds in <tarch. The young spike is lengthened 

 b\ [hv apical growth of its meristematic cap, and 

 graduall}- compresses the adjoining cells of the 

 mother bark into a yellowish layer (Abp). Above 

 iliis dead cell layer, the mother bark is still per- 

 fectly healthy and dies only if ruptured by the 

 gnarl cone. 



In tlie above statements, we ha\e i)aid special 

 attention to the structure of ihe completed gnarl 

 cone, and will now turn to the processes of 

 broadening the medullary rays, which initiate the 

 formation of the gnarl cone. I have studied one 

 such case in Ribes nigrum'^. 

 l"'ig. ()2 h shows the accumulated beady gnarls, up to one millimetre in 

 height, which lie side by side, or partially over-lapping. In the cross-section, 

 Fig. 63, is seen the radiation of the wood ring of the branch, in fan-like 

 or feathery subdivisions, into the body of the gnarl which in this case is 

 not conical, as in Mains sinensis, but resembles a spherical wart. 



Fig. 63 gives at B the longitudinal section, at A the cross-section of a 

 gnarl wart. D is the normal Jixis of the branch w^ith its pith body (w) and 

 wood ring (//), which now seems cleft by the excrescent medullary rays 



Fig-. 62. Bead-like for- 

 mation of gnarls in tlie 

 black currant. 



1 Sorauer, F., Krebs an Ribes nigrum. Zeitschr. f. Pflanzenkiankh. 1891, p. 77. 



