98 PRACTICAL BOTANY 



On following the course of these vascular bundles it will be 

 seen that on entering the stem they proceed at first towards the 

 centre : before reaching it they curve downwards, and finally 

 turning again outwards they approach the periphery of the 

 stem. We thus see that in young stems of Maize the course of 

 the bundles corresponds to the Palm-type, though as the stem 

 grows older, and the internodes develop, the correspondence is 

 less obvious, by reason of the almost straight course pursued 

 by the bundles in the internode, and the complications which 

 arise at the node. 



But no student should be satisfied with seeing the typical 

 bundle-system of a Monocotyledon in small microscopic pre- 

 parations : for it is not difficult to prepare from any of the 

 Palms which have a columnar stem, dissections which shall 

 show plainly to the naked eye the course of the vascular 

 .bundles. The spiral lateral curvature of the bundles in their 

 downward course maybe readily recognized in such dissections, 

 where the ground tissue has been removed to a sufficient 

 depth. No botanic institution should be without such dis- 

 sections, which will make more plain to the mind than any 

 description, or any microscopic preparation, the rather com- 

 plicated bundle-system of the Palm-type. 



ii. STEM ARBOREOUS TYPE. 



I. Examine preparations of the old stem of Yucca or 

 Draccena, in which the thin-walled parenchyma has been 

 allowed to rot away, while the vascular bundles remain. On 

 comparing transverse and longitudinal sections of such stems, 

 it may be seen, with the naked eye 



1. That the central primary bundles are isolated, and that 

 the course of each bundle may be traced as starting from below 

 at the periphery of the stem, then curving towards the centre 

 as it ascends, and finally turning outwards, and passing into a 

 leaf. These are therefore common bundles. 



2. That the peripheral mass of secondary bundles increases 

 in thickness towards the base of the stem, and has no direct 



