66 



bulk and form of these structures are not directly determined by 

 the spaces which the leaves allow : obviously there are other modi- 

 fying causes. It should be added that while hese expanded free 

 extremities graduate into tapering free extremities, not differing 

 from ordinary vessels, they also pass insensibly into the ordinary in- 

 osculations. Occasionally, along with numerous free endings, there 

 occur loops ; and from such loops there are transitions to the ulti- 

 mate meshes of the veins. 



These organs are by no means common to all leaves. 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 Echeveria, in 

 BryopkyUum, they do not appear to exist ; and I have been unable 

 to discover them in Kaianchoe rotundifolia, in Kleinia ante-euphorbium 

 and Jicoides, 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 the 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 leaf 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 Anatomies" 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 to be drawn, is con- 

 nected by vessels with the parts to which liquid has to be carried. 

 There can scarcely be a doubt, then, that in both cases absorption 

 is effected through them. I have met with another such organ, 

 more elaborately constructed, but evidently adapted to the same 



