34 THE PALM-STEM. 



crescent formed by the vessels, that the large vessels come m contact again 

 in front of the bundle of proper vessels. 



The unusual form of these vascular bundles may be an apology for my 

 entering somewhat more minutely into their structure. The vascular bundles 

 of these plants lie in two circles alternating with each other, those of the 

 inner being considerably larger. Each of these vascular bundles is composed 

 of a combination of three vascular bundles : one, the largest of them, situ- 

 ated internally, consists of a crescent of vessels, the most anterior and largest 

 of which are finely dotted reticulated vessels, while only the most posterior 

 and smallest have the form of spiral vessels. The proper vessels belong to 

 this bundle. In front of this occur two vessels of tolerable size, which 

 in many cases are likewise connected by a number of smaller vessels into a 

 crescent, the convexity of which is directed outwards. Behind these vessels 

 lies a second bundle of proper vessels. It is therefore evident that each of 

 these vascular bundles is formed by the blending of two vascular bundles. 

 The structure of the vascular bundles of the outer circle, and of those formed 

 in the slenderest shoots of Tamus Mepliantipes, show clearly that the outer 

 and smaller of these vascular bundles is also composed of two bundles ; 

 for in the vascular bundles of the outer circle, the crescent formed by the 

 vessels of the larger bundle, looking inward, is more widely open, and the 

 anterior vascular bundles separate into two, each of which possesses a bundle 

 of proper vessels at its inner side. In the young shoots of Tamus Mephan- 

 tipes, the structure approaches still nearer to that usual in the Monocotyle- 

 dons, for the smaller bundle is either altogether wanting, or, if present, is 

 likewise divided into two portions, which, however, do not converge toward 

 the large vessels, as in the stem, but have their bundle of proper vessels 

 lying at their inner side. 



In the forms enumerated hitherto, the analogy of the vascular bundle 

 with that of the Palms is so evident as to require no further demonstration 

 in that respect. The forms in which the different vessels exhibit almost 

 equal diameter e. g. in Henierocallis flava, Tulipa gesneriana, Fritillaria 

 imperialist Orchis militaris, Iris sibirica, and Aloe Commelini, are rather more 

 removed ; but here also the most anterior vessels are constantly reticulated, 

 the posterior annular and spiral vessels. 



It may not be superfluous to mention a structure which may readily give 

 rise to errors. In the vascular bundles of many aquatic plants an air-passage 

 occurs, possessing no proper walls ; for example, in Alisma Plantago, Sagit- 

 taria sagittifolia, Scirpus lacustris, Cyperus Papyrus, &c. If merely a trans- 

 verse section of these vessels be examined, this canal may easily be taken 

 for a vessel, as happened with Bernhardi (iiber Pflanzengefasse, p. 16, in 

 Alisma), and Meyen (Phytot. pi. vi, fig. 1, in Scirpus). The whole form of 

 the vascular bundle becomes altered through this canal. In Scirpus and 

 Cyperus this is not so much the case, the vascular bundle being in general 



