DISTRIBUTION OF THE BUNDLES IN THE STEM. 127 



Both lateral strands of a leaf in such a case as this run down 

 through one internode, bend outwards at the node below, and 

 attach themselves to the lateral strands belonging there. 



Suppose, now, that a cross-section of the stem of Clematis is 

 made at the lowest node represented in Fig. 102 ; all the fibro- 

 vascular bundles at that point will be seen in their relative posi- 

 tions, some of them cut squarely off, 

 others oblique!}', according to curves 

 which they make. A cross-section in 

 the internode above would show slen- 

 derer bundles, but all arranged in much 

 the same manner as in the thicker inter- 

 node below ; that is, in a circle. 1 



The circle is made up of fibro-vas- 

 cular bundles which have an inner por- 

 tion of wood ; within the circle is paren- 

 chyma (the pith), and outside of it more 

 parenchyma (the cortex), which can be 

 stripped off with the bast-portion of the 

 central cylinder as bark. 



Compare Fig. 102 with Fig. 103. In 

 the latter, the stem does not exhibit in 

 cross-section the fibro-vascular bundles 

 arranged in a circle : they are more or 

 less scattered ; there is no clearly de- 

 fined central portion nor well-marked 

 outer portion free from them. Hence it 

 cannot be said that such a stem has any 

 distinction of pith, wood, and bark. 



A further distinction may be here 

 noted ; namely, that the bundles in Fig. 

 102 have the power of increasing in 

 thickness, adding new wood and new bast to the primary struc- 



1 Another feature must be attentively studied ; namely, the relation of the 

 forming bundles to the young leaves at the upper part of the stem. One may 

 say the bundles descend from the leaf to the stem, or ascend from the stem to 

 the leaf. But since the development of the leaf part and the stem part of a 

 bundle goes on together, these terms, ascend and descend, should be under- 

 stood to refer to our method of tracing the bundles out, and not to the method 

 of their development. 



fascicles from the third pair of leaves; x, t, fascicles of the fourth pair of leaves; ft, a, 

 y, S, pairs of undeveloped leaves not as yet having fascicles. The diagram illustrates 

 both Clematis Viticella and C. Vitalba. (Nageli. ) 



FIG. 103. Longitudinal section through the stem of Aspidistra elatior, showing the 

 curved course of the flbro-vascular bundles in the simplest palm-type. (Falkenberg.) 



