30 BOTANY PART i 



to the branches becoming long and pendulous. Herbaceous plants 

 often have stems which creep on the surface of the ground. Other 

 plants, both herbaceous and woody, climb upon various supports by 

 means of hooked hairs, prickles, and modified shoots, by means of 

 roots or tendrils, or by twining movements. Climbing plants are 

 termed LIANES, those which wind round a support being distinguished 

 as TWINING PLANTS. It is the presence of numerous rope-like stems 

 of lianes which renders the tropical forest so impenetrable. On both 

 creeping and climbing shoots the leaves tend to become displaced 

 towards the dorsal surface of the stem, while branches spring from 

 the sides and roots from the ventral surface. 



In catalogues and descriptions of plants the duration of the period of growth 

 is usually expressed by special symbols : thus O indicates an annual ; a biennial, 

 and H a perennial herb ; f? is employed to designate both trees and shrubs, and 

 for trees the sign fj is also in use. 



Development of the Leaf. The first appearance of the leaf as a 

 lateral protuberance (Fig. 17 f) on the vegetative cone of the shoot 

 has already been referred to (p. 18). When the 

 apex of a shoot is removed by a transverse 

 section and viewed from above (Fig. 31), the 

 origin of leaves as lateral protuberances is more 

 evident than in a longitudinal section. The 

 embryonic leaf rudiment generally occupies 

 but f a small portion of the periphery of the 

 vegetative cone ; it may, however, completely 

 surround it. In like manner, when the mature 

 leaves are arranged in whorls, the developing 

 protuberances of the rudimentary leaves may 

 form at first a continuous wall-like ring around 

 PIO. si. Apical view of thfi the growing point and only give rise later to 

 vegetative cone of a shoot the separate leaf rudiments. Leaves take their 



of Eiwnvmus iavonicns. i e \ e i i 



(x 12 ) origin only from such parts of a plant as have 



remained in an embryonic condition. A leaf 



never arises directly from the older parts of a plant. In cases where 

 it apparently does so its development has been preceded by the forma- 

 tion of a growing point of a new shoot. The growing point of a 

 shoot has usually 'an UNLIMITED GROWTH, while the growth of a leaf 

 is LIMITED. A leaf usually continues to grow at its apex for a short 

 time only, and then completes its segmentation and development by 

 intercalary growth, which is usually localised near the base. It is true 

 that some leaves, such as those of Ferns, have apical growth and 

 continue to grow for a long time (in some cases, e.g. Lygodium, the 

 growth is unlimited), and bear their pinnae in acropetal order. On 

 the other hand, the leaf-like cladodes, although they are in reality 



