18

THE PALM-STEM.

nearer to the centre the vascular bundle lies, the morethe liber is diminished in mass, till at last it displays onlya very thin crescent, while the size of the woody massincreases in the inverse ratio, the smaller vessels lying atits inner side increasing in number. The bundle ofproper vessels enlarges in similar proportion to those ofthe woody mass. The softness of the whole vascularbundle increases with the diminution of the mass of theliber, because the liber alone contains the thick-walledelementary organs.

Similar changes in the structure of the vascular bundleare met with, when it is dissected out from the stem andexamined in different parts. In this way we may notonly obtain, by comparison of transverse sections of oneand. the same vascular bundle, a survey of the changes ofits size and structure which leaves no room for doubt,but we may detect more readily than in the cross sectionof an entire stem, the changes which the vascular bundleundergoes in its way from the centre of the stem to thebase of the leaf.*

These changes are as follows: the nearer the vascularbundle approaches to the leaf, the more the liber-massdiminishes in size and the woody portion increases, agreat multiplication of the vessels of the latter being con-nected with this, these, however, considerably decreasein size. In the vicinity of the point of emergence fromthe stem, a division of the vascular bundle into several(up to six) portions already begins to be effected, thistaking place in such a manner, that small bundles of liberappear on the outer borders of the woody portion, at itsposterior and lateral surfaces, behind which, and at somedistance higher up, are found the rest of the systems(wood and proper vessels) belonging to a perfect vascularbundle, so that the entire vascular bundle consists of acircle of smaller bundles, which all have their woody por-

* What relates to these two methods of investigation is not a translationof the original text, for the latter referred specially to the illustrations here,and therefore would be incomprehensible without them. (H. v. Mohl.)