44 HOFFMANN ON THE CIRCULATION 



vascular bundle which diverges at certain points from the me- 

 dullary sheath, and runs into the petiole of the leaf which 

 subtends the bud. Subsequently (in the succeeding year), these 

 vessels, which are torn off externally at the fall of the leaf, are 

 covered up and buried by degrees by the new wood formed in 

 the young shoot (produced by that axillary bud) ; but they may 

 still be discovered, even in old branches, if carefully sought. In 

 the above case, in Salix acuminata, it was found that the saline 

 solution had descended in the old main shoot, as mentioned, 

 between the innermost and next succeeding layer of the wood, 

 and thus externally over that little vascular bundle (originally 

 going to a leaf) belonging to the inmost layer of wood. 



Balsamina hortensis. The solution absorbed by the leaves 

 could in three days be traced upwards in all parts and farthest, 

 and downwards in thevessels and the (wood) prosenchyma accom- 

 panying them ; the latter, however, had conducted very much 

 more fluid, since in cross sections the colourless large vessels 

 were ordinarily perceived surrounded by a delicate ring of very 

 small blue cellular points. In another case also, when the plant 

 had absorbed very little of the solution, it was observed that this 

 had descended principally in the internal cortical layer, and in 

 the prosenchymatous cells in the vicinity of the vessels, not how- 

 ever in the latter themselves. 



While, therefore, the tracheae conducted most readily in woody 

 plants,inthe succulent balsam the neighbouring prosenchymatous 

 cells were decidedly overcharged. Perhaps the cause lay in the 

 prosenchymatous cells of the woody plants being in many cases 

 filled with air (which is not the case in the balsam), whereby, 

 of course, the passage of the solution from cell to cell through 

 the, moreover dry, membranes might be rendered more difficult. 



Lactuca sativa. The solution absorbed by the leaf during 

 eleven days was contained in especial abundance in the spiral 

 vessels and their surrounding prosenchyma, on the corresponding 

 side ; on the other side of the stem, however, only in the pros- 

 enchyma surrounding the vessels, and in the lower parts of the 

 stem the same. Here, moreover, the rind and the pith also had 

 conducted, the pith principally in the cells at the boundary of 

 the medullary cavity. 



Euphorbia terracina, L. After four days' absorption through 



