184 Mr. A. Henfrey on some Points in the Structure 



between the two latter is the fistular condition of the stem in 

 the Grass*. 



I next directed my attention to the lower extremities of the 

 fibro-vascular bundles, endeavouring to discover their relations 

 with the fibro-vascular system of the roots. Here we meet with 

 several modifications of arrangement. 



In the stems I have examined the lower ends of the fibres ap- 

 pear to branch and to anastomose with their fellows, sometimes 

 forming a distinct fibrous layer. In order to explain the rela- 

 tions of these extremities, I must point out some peculiarities in 

 the cellular system. 



Von Mohl has described in the stems of Palms a central region, 

 a fibrous layer, and a cortical region. The analogues of these 

 appear to me to be present in most monocotyledonous stems. 

 The tissue of the central region is generally composed of spheri- 

 cal cells which contain abundance of starch at certain periods ; 

 this region, in which lie the fibro-vascular bundles, undoubtedly 

 represents the pith and medullary rays of Dicotyledons. The 

 cells of the cortical region are usually very irregular in form, and 

 have large intercellular spaces; they contain little or no starch. 



In bulbs the central region is inclosed by rather a thin layer 

 of the cortical parenchyma, which is continuous with the bases of 

 the coats or scales; the line of junction of the two regions is in- 

 dicated in the very youngest state of the bulb by a darker colour 

 and greater density of the tissue. At this line the fibro-vascular 

 bundles terminate below, and their extremities, by branching 

 and anastomosing, frequently produce a dense layer, the " fibrous 

 layer " of Von Mohl. The cortical region cannot be made out in 

 the culms of the Grasses, and it is not continued distinctly into 

 the flowering-stems of bulbs. In Sparganium ramosum it is very 

 much developed, both in the nodes and internodes ; in the former 

 it exhibits fibres crossing transversely, and thus weaving, as it 

 were, the whole into a dense fibrous coat separating the central 

 from the cortical region. 



The most important point relating to the fibrous layer is, that 

 it gives origin to the roots, for there is no direct communication 

 between the fibro-vascular bundles of the stems and those of 

 the roots. The bundle which lies in the midst of the root of 

 Sparganium, and indeed of all the annual roots I have examined, 

 is composed of a number of vessels arising in a circle from the 



* An illustration of this analogy between the nodes of the stem of a 

 Grass and bulbs, physiologically denoting a certain degree of independence, 

 seems to me to be offered by the possibility of grafting grasses upon one 

 another at the nodes. Tliis has been effected by an Italian botanist, Calde- 

 rini, in the Millet, and he also successfully grafted Rice upon Panicnm 

 Crus-gatli.—Sce Ann. des Sc. Nat. Sept. 1846. 



I 



