64 ON THE PLANT- CELL. 



be seen without vessels in the longitudinal tissue of many Cryptogamia, 

 as in the Mosses, also amongst the P/ianerogamia, in Mayaca fluvia- 

 tilis, some species of Potamogeton, in jVajas, Caulinia, and Cerato- 

 phyllum ; in short, in all plants growing under water, or which are 

 nourished from their surface and not their roots. The term " vessel" has 

 misled botanists, and it is time that we should be apprised of the fact 

 that there is as much difference between the so-called vegetable vessels 

 and those of animals, as there is between vegetable and animal wings and 

 reproductive germs. The vessels of plants play but a very subordinate part 

 in the functions of vegetable life, and, so far from being special organs for 

 the circulation of the fluids of plants, they are themselves the last pro- 

 duced results of such movements of the sap, and the first parts to become 

 filled up and impervious to the admission of the juices circulating in the 

 plant. Vessels are often found wanting in entire plants, and the most 

 important parts of plants, as in the gemmules and filaments, whilst in 

 other plants closely related to these they are found present. These views 

 of the doctrine of the vascular bundles I first propounded in Wiegmann's 

 Archiv for 1839 (Bd. I. S. 220.).* 



27. E. TISSUE OF THE LIBER ( Tela Jibrosa, Bastgewebe). 

 This is formed of cells so long that they cannot be regarded as cells 

 superimposed upon one another, but as fibres lying close to one 

 another. The walls of these cells are strong, often thickened so as to 

 exclude the transmission of light, without exhibiting a clear confi- 

 guration of the deposit layers. They are mostly soft and flexible. 

 These cells seldom present themselves individually in the pith and 

 the bark : they are more frequently seen in bundles (liber-bundles), 

 in the visible nerves (veins) of flat small leaves, in the projecting 

 angles of stems, and very frequently in the neighbourhood of the 

 vascular bundles on the external side of the cambium ; in the last 

 it is especially called liber. 



F. LIBER CELLS of Apocynacea* and Asclepiadacece. These are 

 peculiarly long, seldom branched cells, with thickened walls, which 

 often exhibit very delicate spiral fibres crossing each other. In 

 some spots their cavity is entirely obliterated, whilst in others they 

 are swollen and vesicular, and contain a true milky juice. 



G. MILK VESSELS ( Vasa lactescentiu), are longitudinal cells, 

 frequently branched in all directions. Sometimes their walls are 

 thin and homogeneous ; at other times, especially from age, they 

 are thickened by layers, and marked in a spiral manner (as in the 

 leafless JZuphorbiacece). They contain a colourless or variously 

 coloured milky juice. 



There are few departments of botany that offer more unanswered 

 questions, and that demand greater research, than the subjects of the 

 three preceding paragraphs. 



The fibres of the liber in the youngest parts of the bud in which they 

 can be seen are very short, almost spindle-shaped, cells, which lie with 

 their sharp ends pushed between each other, so that as the part to which 

 they belong increases in length, so do they increase also, but are brought 



* This paper is also printed in Schleiden's Botanische Beitrage, vol. i. p. 29. ; and has 

 been translated in Taylor's Scientific Memoirs, and by the Sydenham Society. TRANS. 



