34 



BOTANY OF THE LIVING PLANT 



Clematis in Fig. 20. Here the leaves are arranged in pairs, and from 

 each leaf three vascular strands pass into the stem. Each strand curves 

 downwards before reaching the centre of the stem, and after taking 



a straight downward course to the 

 level of the next pair of leaves it 

 forks. The two shanks are then 

 inserted right and left upon the 

 strands that enter there. If a trans- 

 verse section be cut at any point 

 between the pairs of leaves, the 

 section shows six main strands 

 arranged in a ring, with smaller 

 strands between them (Fig. 21). A 

 very simple connected system of 

 vascular strands is thus formed, and 

 it illustrates the arrangement usual 



Clematis viticella. End of a branch 

 which has been made transparent by 

 the removal of the superficial tissues 

 and treatment with caustic potash. The 

 emerging strands have been slightly dis- 

 placed by gentle pressure. The two 

 uppermost pairs of young leaves (bl l , bP) 

 are still without leaf traces; v, apical 

 cone. (S. after Naegeli.) 



FIG. 21. 



Transverse section of an internode of a stem of 

 Clematis, showing a ring of six larger and six smaller 

 vascular strands, surrounding the central pith, and 

 covered externally by the thick cortex. The collen- 

 chyma massed at the projecting angles is dotted. 



for them in the shoots of Dicotyledons. There are differences in the 

 number of the strands entering from each leaf in various examples. 

 In some there is only one strand, in others more. The arrangement 

 of the leaves on the stem may also vary, as well as the distance 



