STRUCTURE.] PITH OF NODES. 191 



few modifications. I sought on a Walnut Tree a branch 

 whose young shoot was very long. The terminal bud was 

 separated from the last leaf but one by an internode of nine 

 centimetres in length. Then came a leaf at five centimetres 

 distance, and another eleven centimetres lower down. On 

 this branch the pith was full at twelve centimetres lower 

 than the terminal bud ; but at each leaf, bearing a bud in its 

 axil, the pith was perforated by some lenticular cavities. Here 

 the action of the bud is evident, and better proof could 

 not be brought that it is to the absorbing action of the 

 bud that we owe the division of the pith into discs. I cut 

 this long branch into two and dried it. The next day the 

 compact pith had lost its liquid to so great a degree that the 

 stem was hollowed into a gutter ; the slits were greatly in- 

 creased, but the membrane formed by the pith was also seen 

 dried up and covering the bottom of the gutter formed by 

 the half of the stem slit longitudinally ; this membrane was 

 also raised by as many hollow vesicles as there would have 

 been lenticular cavities if the stalk had remained entire ; 

 here is a manifest proof that there is in the constitution of 

 the pith a predisposition to separate thus into discs, and this 

 predisposition consists in nothing more than the manner in 

 which the layers of the cells are placed." (See additional 

 observations and anatomical figures in the work above 

 referred to.) 



Sometimes the pith is more compact at the nodes than in 

 the internodes, as in the Ash; whence an idea has arisen 

 that it is actually interrupted at those places : this is, however, 

 a mistake ; for in general there is no interruption of conti- 

 nuity, but a mere alteration in compactness. It does however 

 sometimes happen, that the pith takes a large development 

 at the nodes, so as to interrupt the vascular system of the 

 internodes. This occurs in what are called articulated stems, 

 as in Piper, &c., and in the Vine when young. Dutrochet 

 regards such cases as evidence that each internode is an inde- 

 pendent creation in the beginning, and that it is only after 

 having been growing for a period of time, varying in dif- 

 ferent cases, that the internodes become connected by woody 

 formations. The Miseltoe, however, on which he relies for 



