590 APPENDIX C. 



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 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 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 Semper vivum^ in Echeveria, in 

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

 to discover them mKalancho'e rotundifolia, in Kleinia ante-euphor- 

 bium 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 func- 

 tions 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 interest- 

 ing 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 termina- 

 tions, 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 Anatomicae " 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 



