24 THE FLOWERING PLANT. 



many climbing and creeping plants. On the other hand, the 

 internodes may be so extremely short as to make the stem a 

 scarcely recognisable stump, the leaves being at the same time 

 crowded into a tuft or rosette. Good examples are daisy, dande- 

 lion, and house-leek. Such an abbreviated stem is sometimes 

 termed a root-stock, while the leaves growing from it are radical, 

 the old (but erroneous) idea being that they grew from the root. 

 It may also happen, as in the buttercup, that the internodes are 

 very short in the lower part of the stem only. The leaves borne 

 by that part are then also called radical. 



The thickness of a stem is dependent on other conditions besides 

 the state of the internodes. Perennial gymnosperms and dicoty- 

 ledons (rarely monocotyledons) undergo an annual increase in 

 thickness, and many stems and branches, particularly underground 

 ones, are thickened in connection with the storage of reserve 

 materials. 



The chief factor determining the general shape of a stem 

 system is the nature of the branching. This is monopodial, as in 

 the case of the root, and two kinds may be distinguished: (i.) 

 Racemose, where, as in most cases, the main axis continues to 

 grow, and is larger and longer than its branches, which, in their 

 turn, bear a similar relation to its subordinates. The pyramidal 

 outline of many trees, e.g., firs, is due to this cause. (2.) Cymose, 

 where the main and other axes cease growing after a time, and 

 are outstripped by their branches. This may result in false 

 dichotomy, i.e., apparent forking, as in the mistletoe; or a pseud- 

 axis or sympodium may be formed, where the direction of an axis 

 is continued by one of its branches, which after a certain time is 

 supplanted by one of its branches, and so on (cf. p. 48). The 

 name pseud-axis is given because, at first sight, we have to deal 

 with a case of racemose branching. Examples are found in the 

 twigs of elm and beech. The main branching of these trees is, 

 however, racemose. Special branch systems or inflorescences are 

 often developed, upon which the flowers are borne. These will be 

 dealt with later on in connection with the flower. 



The last important point which determines the shape of the 

 stem is its direction, whether vertical, horizontal, or otherwise. 



In giving a brief account of various stems, it will be convenient 

 first to speak of aerial forms and then to proceed to subterranean 

 ones. 



Aerial Stems. — As already mentioned, the typical overground 

 main stem is erect and self-supporting. This requires a consider- 

 able amount of strength, which may be gained by size and solidity, 

 as in tree-trunks, or where there is comparatively little substance 

 this may be disposed in the most advantageous manner, i.e., on 



