Vegetable Physiology for the Year 18S6. 529 



which contain such vessels are a great deal too thick to be 

 immediately observed without any dissecting. Such a motion 

 of the resin would place the receptacles nearer to the true 

 vital sap vessels; and I consider it as highly probable that 

 they are of an importance much greater than we have hitherto 

 dared to ascribe to them ; for the resinous ducts in the Conifer ce, 

 as well as the gummy ducts in the Cycadece, form a system, 

 of itself entire, and perhaps continuous through the whole 

 plant; and it is exactly in those plants where these resinous 

 ducts occur that the vital sap-vessels are wanting. A great 

 coincidence may also frequently be proved, between the saps 

 of the gummy passages and the vital sap-vessels of various 

 plants, in a chemical point of view. 



Link remarks on the milk vessels of the Euphorbiacece and 

 Asclepiadece, that they stand singly in the stem, are straight 

 and simple, and appear ramified only in the young stems 

 where they run out towards the leaves ; they were also observed 

 in shrubby Euphorbia with spreading branches; sometimes 

 they keep on their course at some distance from the nerves. 

 Link further says that they terminate with an obtuse point; 

 they also exhibit no anastomoses, nay at times they appear to 

 have transverse partitions, but only false ones. These obser- 

 vations, it is true, do not exactly coincide with those which 

 I mentioned in the report for 1835, with a view to refute the 

 objections of Treviranus. I yet hope to succeed in giving to 

 many of them quite a different bearing. In no plant is it more 

 easy to observe than in the leaves ofHoya carnosa that the ra- 

 mified and very thick membranaceous vessels with obtuse ends 

 traverse the diachyma ; these vessels, however, are not milk- 

 sap vessels, but they are ramified cells of the liber, or fibrous 

 vessels of which hitherto no mention has been made in botanical 

 writings. A structure so highly remarkable belongs to the 

 fibrous vessels (fibrous cells) of the Asclepiadece and Apocynea, 

 of which mention has already been made. But nowhere is the 

 ramification and anastomosis of the vessels of the stem to be 

 observed more evidently and frequently than in the stem of 

 the old genus Sarcostemjna ; here we find the regular and 

 manifold anastomosing tissue of the milk vessels deposited 

 immediately before the layer of the cells of the liber, which 

 exhibit in every respect one and the same structure with those 

 ramified vessels in the leaves of the Hoya, with the exception 

 that ramification is wanting in them. These observations 

 evidently show in the most certain manner that Mirbel's state- 

 ment* that the cells of the liber in Nerium, where the ap- 



* Vide our Year's Report for 1835. 

 Third Series. Vol. 1 1. No. 70. Dec. 1837. 3 Y 



