84 BOTANY PART i 



As in many thalli the surface of the cormus is considerably in- 

 creased by branching. The shoot forms lateral branches, the roots 

 give rise to lateral roots, and by this branching, which in many plants 

 begins even in the embryo, a shoot-system and root-system arise. 



The term cormus is usually employed as equivalent to shoot to denote a leafy 

 stem apart from the roots, and a shoot or cormus is then recognised in the leafy 

 Bryophyta. This view, however, dates from a period when the life-history of the 

 Bryophyta was not accurately known. It is now established that the "shoot" of 

 the Moss is not homologous with the shoot of the higher plants. It is therefore 

 advisable not to employ the terms shoot or cormus in speaking either of the 

 Bryophyta or of similarly organised Algae. There is nothing to prevent using the 

 conception of the cormus as a wider one than that of the shoot, and to understand 

 by it the vegetative organs of the cormophytes differentiated into shoots and roots. 

 Further, there are transition forms between roots and shoots (e.g. the rhizophores 

 of Selaginella) and between leaves and shoots (e.g. Utricularia). 



1. Construction of the Typical Cormus 



The fundamental organs of those cormi which can be regarded as 

 typical will be considered in the first place. Their peculiarities only 

 appear typically in such plants as our native trees, or even more 

 clearly in many herbs. The fundamental organs may undergo many 

 modifications and, in extreme cases, their distinction may be difficult. 



(a) The Shoot 



The shoot in land plants may be wholly or in part exposed to the 

 air (AERIAL SHOOT) or be partly buried in the soil (SUBTERRANEAN 

 SHOOT, Fig. 138); the latter is the case in many perennial herbaceous 

 plants (cf. Figs. 123, 138). It consists of the STEM or AXIS of the 

 shoot and the LEAVES. The latter on. the aerial shoots, which are 

 usually green, are developed as foliage leaves, while on the white or 

 colourless subterranean shoots (root-stocks or RHIZOMES) they are 

 mere scales. The stem bears the leaves and provides for the extension 

 of the shoot-systems ; this involves the elongation of the stem and 

 the formation of new leaves and lateral branches, the connection 

 between the leaves and roots, and the conduction of material between 

 these organs. The stem in most subterranean shoots further serves 

 as a place of storage of reserve materials. The foliage leaves, like the 

 leaf-like branches of thalloid plants, are the organs of assimilation and 

 transpiration in the cormophytes. The external form and internal 

 structure of the foliage leaves and stem stand in relation to these 

 functions. 



(a) The Growing 1 Point. The shoot grows by means of an apical 

 growing point situated at the extreme tip of the stem. Since the 

 growing point is extremely small and scarcely visible to the naked 

 eye, it is best seen when longitudinal sections of the apex of the shoot 



