LEAVES II 



Adventitious Shoots. — Lateral shoots may arise on some 

 flowering plants in places other than the axils of leaves. Such 

 shoots are said to be adventitious. For instance, adventitious 

 shoots may burst out from the roots of Poplars, Rose-trees, 

 Hazels, and raise themselves above the surface of the soil. 

 Again, adventitious shoots may spring from cut fragments of 

 Dandelion-roots, or from Begonia-leaves pegged down to 

 produce cuttings. When young branches shoot out from 

 older parts of tree-trunks they are often axillary branches, 

 and their appearance is merely due to the sudden activity 

 of resting-buds which were formed years before. But in 

 the case of Willow-trees from which the upper shoots have 

 been lopped, many entirely new lateral buds arise on the 

 upper part of the trunk. These grow out to form branches 

 which are adventitious, because they are not due to the de- 

 velopment of resting axillary buds. In all these cases of 

 adventitious branching the shoots produced have stems and 

 leaves, and therefore are shoots. 



ARRANGEMENT OF THE LEAVES. 



The leaves are attached to the nodes of the stem. On 

 the stems of some plants (e.g. Buttercup, Wallflower) no two 

 leaves are inserted at the same level on a simple stem — that 

 is, there is only one leaf at each node. This leaf-arrange- 

 ment is described as alternate or, better still, as spiral 

 {acyclic). On other stems two or more leaves are attached 

 at the same level and at the same node of a stem. The 

 leaf-arrangement is then described as nihorled {cyclic), 

 and the collection of leaves at each node constitutes a 

 whorl. 



Whorled (Cyclic) Leaves. — In this leaf-arrangement the 

 leaves at a single node are disposed in a very regular 

 manner. They are inserted in such a way that the 

 angular distance between each two adjacent leaves is the 

 same. Thus, if there be two leaves at the node, they are 

 inserted on the opposite sides of the stem (say the north 

 and south sides), as in the Chickweed (fig. 43) and Dead 

 Nettle; if there be four leaves, they are ranged like the 

 four points of a compass (say N. S. E. W.) ; if there be 

 three leaves at a node, each is separated from its neighbour 



