82 Prof. C. Morren on the discoid Piths of Plants. 



cone^ as if the removal of the nutritive matter first took place 

 there. 



The compact pith in the walnut tree is composed of a num- 

 ber of small cells nearly in the form of cubes^ all equal to one 

 another, white, transparent, having very few globules, but 

 containing at a very early period masses of small crystals, or 

 true muriform calculi, which occupy the centre of the cells. 

 At a later period, when the pith separates into discs, and dies, 

 the cells undergo very 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, as may be seen at A. fig. 7» Here 

 the action of the bud in emptying the pith is fuUy evident, 

 and a better proof could not be brought that it is really 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 

 increased, 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 vesicules 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 predispo- 

 sition consists in nothing more than the manner in which 

 the layers of the cells are placed. 



Figure 8. shows what happens when the pith is regularly 

 exhausted by the suction of the bud. Then such regular discs 

 form with two or three (or even more) roots and intermediate 

 discoid cavities (e,/, fig. 8.). A part of the pith adheres to 

 the ligneous tube and does not split {d, fig. 8.). 



I examined the discs formed by this old, dry, dead pith. 



