36 METAMORPHOSED SHOOTS 



termed tendrils (figs. 57, 59). A tendril is a simple or 

 branched string-like irritable* structure which is capable of 

 coiling round, or fixing itself to, suitable objects. Tendrils 

 and other irritable climbing organs can embrace slender 

 supports which are horizontal in position. The leaf-stalks of 

 the garden Tropmolum and of Clematis, also the finely-divided 

 leaves of the Fumitory, act like tendrils and coil round slender 

 stems. 



(iv.) Scramblers do not adopt any of the methods above 

 mentioned; they merely lean against or scramble over other 

 plants. Some clamber up by the aid of hooks or prickles, as 

 in the case of Galium (Cleavers) and Rubus (Brambles). 



SUBSIDIARY OUTGROWTHS (Hairs, etc.). 



So far we have mentioned roots, stems, and leaves, but have 

 given no account or explanation of the hairs, hooks, and prickles 

 scattered over various parts of plants. We have learnt that 

 roots, stems, and leaves all arise, and are arranged, in accord- 

 ance with certain definite laws. Furthermore, they are recog- 

 nisable by their structure. The hairs, prickles, etc., which are 

 irregularly arranged over the plant, cannot be regarded as being 

 roots, stems, or leaves, because they do not occupy the definite 

 positions assigned to these members. In particular, hairs are 

 found on roots, stems, and leaves : prickles occur on leaves 

 and stems ; these structures are not axillary in position, nor do 

 they have buds in their axils. We therefore require a term 

 to include all outgrowths which are neither roots, stems, 

 nor leaves, but are, more or less, irregularly disposed on 

 those members. We may term these structures ^'subsidiary 

 outgrowths." [In the majority of text-books "subsidiary out- 

 growths" are referred to under the heading of "hairs and 

 emergences"; but it is impossible to give the corhplete defini- 

 tion of a hair or an emergence without assuming a knowledge 

 of microscopical botany.] 



METAMORPHOSED SHOOTS. 



Stems and leaves assume many different forms, and they 

 may present appearances so changed, or metamorphosed, as to 



*See the section on Physiology. 



