332 



FORM AND POSITION OF THE TRANSPIRING LEAVES AND BRANCHES. 



In the Casuarinese and in Cytisus radiatus (see fig. 69), the green tissue is distri- 

 buted in the cortex of the branches exactly as in the case just described; but the 

 strips of green tissue traversing the stem are deeply cut into by longitudinal 

 furrows. In some other leafless switch-shrubs, such as species of the genus 

 Ephedra, the chlorenchyma forms a continuous and uniform mantle round the 

 stem, uninterrupted by strips of bast. But in this case the stomata are distributed 

 uniformly over the whole surface of the rod-shaped branches, while in the brooms, 

 Casuarinese, and in Cytisus radiatus they are absent from those portions of the 

 epidermis which cover the strips of hard bast. 



Plants with leaf-like branches or cladodes are distinguished from switch-plants 



r^^-r 







Fig. 81.— Switch-shrubs. 

 1 Part of stem of Spar/mm scoparium cut transversely; x30. 2 part of the transverse section ; x240. 



by the fact that all their shoots are not circular in section, but some are flattened, 

 looking as though they had been pressed out. When this flattening is restricted to 

 the so-called " short branches ", i.e. when on a stem only the ultimate, comparatively 

 short branches are flattened, the main axes remaining cylindrical, like ordinary 

 stalks, these structures have quite the appearance of leaves which are sessile on the 

 rounded stems. This explanation of them, however, given by botanists, is not at 

 first sight satisfactory to the uninitiated. Why should these flat green structures be 

 branches, and not leaves? The illustration opposite at once makes the matter clear. 

 It represents two cladode-bearing plants, viz. two species of Butcher 's-broom (Ruscus 

 Hypoglosswm and aculeatus), each at an early stage of development and also when 

 fully grown. On the young shoots, which have just made their way out of the soil 

 (see figs. 82 ^ and 82 ^), the true leaves can be seen in the shape of small sessile pale 

 scales on the long, rounded, finely-ridged axis; and from the angles which these scales 

 make with the long axis arise darker, much thicker organs which rapidly increase 

 in size, while the supporting covering-scales become dry, shrivel up, and finally 



