BOTANY FOR BEGINNERS 



CHAP. 



leaves have the veins finely divided so as to give mechanical 

 support, as well as to expose as great a surface to the water as 

 possible. In the case of marsh plants like the water Crowfoot, 

 which has two kinds of leaves, it is only the submerged ones 

 which are divided. 



Ex FT. 27. Collect a number of leaves and arrange them into 



(i) Two series according to their venation. 



(ii) The two divisions, unicostate and multicostate. 



Arrangement of Leaves on the Stem. Leaves grow 

 from the nodes of the stem, and the arrangement of these 



FIG. 38. Alternate leaves of 

 Rhododendron. 



FIG. 39. Opposite leaves of 

 Privet. 



depends upon the length of the internodes and the size of the 

 leaves. The leaves on a given plant are always inserted at 

 points which bear a certain relation to one another, which may 

 be expressed in a numerical manner. The arrangement of 

 leaves on a stem is often spoken of as phyllotaxis. If one 

 leaf only is produced at a given node, and from the node higher 

 up the stem but on the opposite side another springs the 

 phyllotaxis is said to be alternate, as in the Wallflower. 



