12 



A cladode is a stem coloured green, with, or without, 

 inconspicuous scale leaves, which more or less resembles a leaf 

 and performs the functions of a leaf, e.g. the stem of the 

 prickly pear, Opuntia Dillenii. 



Branching. 15. Branching, i.e. the pro- 



duction of new stems from the parent stem, takes place in two 

 principal ways termed, respectively, dichotomous and lateral 

 branching. In the first the growing point of the parent 

 stem divides into two ; two branches of equal vigour are thus 

 formed, as in a two-pronged fork, and there is no continuous 

 main axis. This method of branching is very rare. 



In lateral branching the growing point of the parent stem 

 does not divide and new stems are developed laterally from the 

 parent. There are two principal kinds of lateral branching, 

 the monopodial and cymose. In the former there is a distinct 

 and simple main axis, formed by the elongation of the parent 

 stem. Such a main axis is termed a monopodium. Such a 

 system of branching is well seen in a Pine tree in which the 

 leader has uninterruptedly developed from the terminal bud. 



In cymose branching there is no simple main axis formed 

 by the elongation of the parent stem and the lateral branches 

 grow faster, or for a longer period, than the parent. Of this 

 form of branching there are two types, the sympodial and 

 falsely di- or tri-chotomous. In sympodial branching there is a 

 main axis but this, instead of being a simple axis consisting of 

 the parent stem, is built up of the basal portions of a number 

 of lateral branches. On each segment of such an axis, one 

 lateral branch develops more vigorously than any other, i.e. 

 there is one leader. The axis so formed is termed a sympo- 

 dium, or false axis, and is at first crooked but frequently 

 straightens subsequently, see Fig. 3, Plate II. This may often 

 be seen on the twigs of trees the terminal buds of which have 

 died, or not developed vigorously, and the leaders have been 

 formed by the axillary and therefore lateral buds. In false- 

 ly dichotomous branching, such as occurs for instance in 

 Rhamnus virgatus, the branches are forked and at first 

 sight there appears to have been a division of the grow ing point 

 of the parent stem. On closer inspection it appears that in 

 this plant the growing point really terminates in a spine and 

 that there is no dichotomy. In some plants the terminal 

 bud becomes a flower, and in others it dies, or does not develop. 

 A system of branches each one of which forks in this way 

 and produces a pair of lateral branches of equal vigour 



