10.] CHAPTER 11. -SPECIAL MORPHOLOGY OF THE MEMBERS. 39 



(foliose Jungermanniaceae), and of all Mosses; the sporoplijte of 

 Vascular Cryptogams and Phanerogams. 



The distinction between stem and leaf is not, however, obvious 

 in all these plants. In the lower forms, this is due to the low 

 degree which the morphological differentiation has attained ; whilst 

 in the higher forms it is due to the degenerate development- 

 amounting in some cases to complete suppression of the leaves ; 

 and also, in some cases, to the assumption of a more or less leaf- 

 like form by the stem or its branches. The true morphological 

 nature of the members can only be ascertained, in these cases, by 

 a study of their development and of their relation to each other. 



In plants which live for more than one year, the shoot may 

 either persist from year to year, or it may die down to the surface 

 of the soil in each year, the subterranean parts being alone per- 

 sistent. Shoots which last only one year are termed annual. 



The general form of the leafy shoot varies widely. Even on 

 one and the same plant there may be different forms of leafy 

 shoots, the differences being due either to peculiarities in the- 

 conditions of development, or of function. Marked differences 

 exist, for instance, between submerged or subterranean and 

 aerial shoots ; also between vegetative shoots and those bearing 

 the reproductive organs. 



The form of the shoot depends largely upon the amount of 

 elongation which the internodes of the stem undergo. Thus, there- 

 is in some plants (e.g. some Florideae ; Sphagnum, and other 

 Mosses ; the Larch, Pine, and Taxodium, among the Coniferae ; 

 and many Angiosperms) a well-marked distinction of two forms 

 of vegetative shoots. These are the ordinary elongated branched 

 shoots ; and short shoots, termed dwarf-shoots, which elongate but 

 little, branch scarcely at all, and are frequently of but short 

 duration (see p. 19). Thus, in some plants (e.g. many pleurocar- 

 pous Mosses; most Ferns, Conifers, and many other plants) the 

 primary shoot continues to grow throughout the life of the plant ; 

 whilst in others, the growth of the primary shoot is limited, 

 the further development of the shoot being effected by a lateral 

 branch, itself of limited growth ; so that, by the repetition of this 

 process a cymose branch-system is produced (see p. 35). This 

 mode of development by innovation occurs in many so-called 

 uniaxial plants whose primary shoot terminates in a flower; also 

 in the acrocarpous Mosses where the elongation of the shoot is 

 arrested by the development of the sexual reproductive organs, 



