424 MR. SPENCER ON CIRCULATION AND 
are not directly determined by the spaces which the leaves allow: obviously there are 
other modifying causes. It should be added that while these expanded free extremities 
graduate into tapering free extremities, not differing from ordinary vessels, they also 
pass insensibly into the ordinary inosculations. Occasionally, along with numerous free 
endings, there occur loops; and from such loops there are transitions to the ultimate 
meshes of the veins. 
These organs are by no means common to allleaves. In many that afford ample 
spaces for them they are not to be found. So far as I have observed, they are absent 
from the thick leaves of plants which form very little wood. In Sempervivum, in Eche. 
veria, in Bryophyllum, they do not appear to exist ; and I have been unable to discover 
them in Kalanchoé rotundifolia, in Kleinia ante-euphorbium and ficoides, in the several 
species of Crassula, and in other succulent plants. It may be added that they are not 
absolutely confined to leaves, but occur in stems that have assumed the functions of 
leaves. At least I have found, in the green parenchyma of Opuntia, organs that are 
analogous though much more rudely and irregularly formed. In other parts, too, that 
have usurped the leaf-function, they occur, as in the phyllodes of the Australian Acacias. 
These have them abundantly developed; and it is interesting to observe that here, where 
the two vertically placed surfaces of the flattened-out petiole are equally adapted to the 
assimilative function, there exist two layers of these expanded vascular terminations, one 
applied to the inner surface of each layer of parenchyma. 
Considering the structures and positions of these organs, as well as the natures of ihe 
plants possessing them, may we not form a shrewd suspicion respecting their function ? 
Is it not probable that they facilitate absorption of the juices carried back from the lal 
for the nutrition of the stem and roots ? They are admirably adapted for performing 
this office. Their component fibrous cells, having angles insinuated between the cells of 
the parenchyma, are shaped just as they should be for taking up its contents; and the 
absence of sheathing tissue between them and the parenchyma facilitates the passage of 
the elaborated liquids. Moreover there is the fact that they are allied to organs which 
obviously have absorbent functions. I am indebted to Dr. Hooker for pointing out the 
figures of two such organs in the “ Icones Anatomic” of Link. One of them is from the 
end of a dicotyledonous root-fibre, and the other is from the prothallus of a young 
Fern. In each case a cluster of fibrous cells, seated at a place from which liquid has 1 
be drawn, is connected by vessels with the parts to which liquid has to be carried. The 
can scarcely be a doubt, then, that in both cases absorption is effected through them. : 
have met with another such organ, more elaborately constructed but evidently adapted 
the same office, in the common Turnip-root. As shown by the end view and a 
tudinal section in figs. 6 and 7, this organ consists of rings of fenestrated 
arranged with varying degrees of regularity into a funnel, ordinarily having its à 
directed towards the central mass of the Turnip, with which it has, in some purs” 
least, a traceable connexion by a canal. Presenting as it does an external porous re] 
on one of the branches of the vascular system, each of these ee | 
the plant m = ery rapidity the nutriment laid by in the Turnip-root, 2D ogie 
en it sends up its flower-stalk, Nor does even this exhaust the 
