APPENDIX. 55 



the circumference of the stem diminishes, the upper part of 

 the vascular bundles must also follow the leaf, and, there- 

 fore, those vascular bundles which enter the sides of the leaf, 

 instead of being directed in a radial direction to all sides 

 of the stem, as in the perfectly amplexicaul leaf, are only 

 curved towards the arc of the circumference of the stem, 

 on which the leaf is inserted, and since the lower part of 

 each vascular bundle retains its position more or less un- 

 changed, the result is the described condition of a double 

 curvature, downwards and to the side. The greater the 

 difference between the circumference of the stem and the 

 breadth of the base of the leaf, the shorter the internodes, 

 the greater must be this divergence ; hence it is greater in 

 Dracaena than in Yucca,iu Yucca it is greater than iiiAletris. 

 Before I go further into the detail of Meneghini's 

 theory, it will be advantageous to test the facts on which 

 it rests. In this I pass over the question whether the 

 leaves do originate under the form of closed funnels, or 

 not, as this has no essential influence on the theory. The 

 only essential question is, whether or not the breadth of 

 the base of the leaf does gradually diminish its proportion 

 to the circumference of the stem with the age of the latter. 

 That such a change must lead to the alteration in the 

 course of the vascular bundle which Meneghini has 

 deduced from it, does not admit of a doubt ; at all events, 

 if it be presupposed that at the time when this change 

 takes place, the vascular bundles running to the younger 

 leaves, which cross those of the leaf that has begun to 

 change its position, do not oppose any hinderance to the 

 movement of the latter. I believe that this certainly 

 must be the case, and this circumstance alone already 

 makes the theory of the Paduan phytotomist appear 

 untenable ; if, however, we even overlook this, there exist 

 other, more definite reasons, which show that the unequal 

 growth of the leaf and the circumference of the stem 

 do not occur in the way Meneghini has represented. 

 According to his statements, this process is most clearly 

 to be seen in Dracaena Draco, for the leaves, or their 



