176 



BOTANY 



PART I 



The majority of our native cormophytic plants show such pro- 

 tective arrangements against an unfavourable season. In the favour- 

 able period they resemble hygrophytes in not requiring any special 

 protection against excessive transpiration, but they behave as extreme 

 xerophytes during the unfavourable period. Such plants are spoken 

 of as tropophytes. 



The plants of periodically moist climates may be perennial woody 

 plants (trees and shrubs), perennial herbaceous plants, and annual 

 herbs. Each of these groups exhibits special means of protecting 



the transpiring surface and the embryonic 

 tissues against drying. 



1. The woody plants (with the ex- 

 ception of a few evergreens with xero- 

 phytic leaves, such as Ilex, and the Corii- 

 ferae) shed their leaves. The evergreen 

 and the deciduous forms alike contrast 

 with many tropical plants in protecting 

 the growing points within WINTER BUDS 

 (Fig. 202). 



kits 



Such buds are protected by the BUD-SCALES 

 which are in close contact. These may be derived 

 from entire primordial leaves that remain unseg- 

 mented but more commonly are formed from 

 the enlarged and modified leaf-base. The upper 

 portion of the leaf may scarcely develop or may 

 be recognisable at the tip of the bud-scale in a 

 more or less reduced condition. Thus in an 

 opening bud of the Horse Chestnut (Aesculus 

 FIG. 202,-Winter buds of the Beech Mppocastanum) in the spring the small leaf- 

 (Fagus silvatica). kns, Bud-scales, blade can be clearly seen in the case of the inner 

 (Nat. size. After SCHENCK.) bud-scales, while it is scarcely visible on the outer 



scales. In other cases (e.g. in the Oak) the 



bud-scales arise from stipules and thus also belong to the leaf-base. The base of 

 a subtending leaf may remain and cover the axillary bud after the rest of the leaf 

 is shed. 



Bud-scales are thick, leathery, and hard, and usually brown in colour. They 

 are rendered even more effective in protecting the buds from desiccation by corky 

 or hairy coverings, by excretions of resin, gum, or mucilage, and by the enclosure 

 of air between the scales. Resin, etc., are usually secreted by peculiar, stalked, 

 glandular hairs or COLLETERS (cf. Fig. 56) ; in the case of the winter buds of many 

 trees (e.g. the Horse Chestnut) a mixture of gum and resin is thus secreted and, 

 becoming free on the bursting of the cuticle, flows between the scales, sticking 

 them together. When the buds open in the spring the bud-scales as a rule are 

 shed. The internodes between them being very short, the scales leave closely 

 crowded scars on the shoots by the help of which the growth of successive years 

 can be recognised. 



2. The perennial herbs sacrifice not only the leaves but whole 

 leafy shoots with their buds, so far as these project in the air and are 



