254 PHYSIOLOGICAL BOTANY. 



with conical, sheathing-leaves which arise from the peri- 

 phery of the axis, and these, as well as all the subse- 

 quently formed leaves, derive their vessels from the axis, 

 the very earliest development of vessels must be peri- 

 pheral ; and this method of succession is preserved, as 

 long as any leaves continue to be formed. Moreover, 

 the upper end of the vascular bundle, says the author, 

 tends towards the base of the leaf, the lower end becomes 

 elongated obliquely downwards in the form of a delicate 

 filament, consisting of parenchyma, but which never 

 extends into the root. The spots from which the vas- 

 cular bundle arise at the summit of the bud, are organi- 

 cally predetermined : they are there placed with their 

 upper ends converging obliquely towards the centre, and 

 become elongated in both directions i. e. grow both 

 downwards and upwards. The spot at which the upper 

 end of the vascular bundle passes to the leaf, is situated 

 either on the same side of the stem as that in which the 

 course of the vascular bundle is chiefly included, or oppo- 

 site the point of origin of the vascular bundle, obliquely 

 as regards the diameter ; in which latter case, the vas- 

 cular bundle traverses the entire stem obliquely. As the 

 summit increases in length and thickness, each vascular 

 bundle crosses another bundle, either in the interior of 

 the stem or nearer to the periphery, at the point where, 

 either ascending almost perpendicularly, or suddenly taking 

 a horizontal direction outwards, it enters into the leaf. 

 These are, undoubtedly, the most valuable remarks which 

 have been made upon this subject, and I am glad to 

 find that they confirm what I have stated previously, 

 though less completely. Still I must confess that I am 

 in doubt regarding the growth of the vascular bundles 

 upwards and downwards. The author's explanation does 

 not contain any proof of the occurrence of this growth 

 in both directions. In my opinion it always occurs 

 upwards, but in the same manner as is seen in the corm 

 at the base of the young stem, except that the bundles 

 cross at smaller angles as the growth of the stem pro- 



