20 



PART 



-THE MORPHOLOGY OF PLANTS. 



[3. 



from the growing-point of the parent member, whether the 

 growing- point be apical or intercalary (as in Ectocarpus and 

 other Phseosporese (Fig. 7) ; in other words, they are developed 

 exogenously. This is always true of leaves, but there are cases in 

 which normal branches are developed from internal cells of the 

 growing- point, and have therefore to penetrate the external layers 

 of tissue before reaching the surface (e.g. Polyzonia, Amansia, 

 Vidalia, R/hytiphlcea among the Red Seaweeds). 



When, as is commonly the case, the leaves are formed in rapid 



succession at the growing- 

 point of a developing leafy 

 shoot, it makes its appear- 

 ance in the first instance as 

 a bnd, consisting of a short 

 axis bearing a number of 

 young and still small leaves 

 closely packed together. In 

 consequence of the more 

 active growth at this stage 

 of the under (dorsal) sides 

 of the leaves, they bend 

 over the apical growing- 

 point of the shoot, and over- 



\ ^ Wllllllflllll I / lap each other ' Commonl y 



\ _1 Uf 1 some of the external leaves, 



or portions of them, are 

 modified into bud-scales for 

 the protection of the bud. 

 As a rule the leafy branch 

 does not develope in the 

 first year beyond the bud-stage. 



Buds may be distinguished, according to their position, as 

 terminal or lateral; but it must be borne in mind that a bud 

 which is lateral on the parent shoot is the terminal bud of a 

 lateral shoot. Sometimes the primary shoot of the embryo has a 

 terminal bud, which is designated the plumule. The terminal bud 

 may either pass gradually over into the fully grown portion of the 

 shoot behind it, as in the herbaceous shoots of annual plants ; or 

 it may be sharply marked off from the older part of the shoot, as 

 may be clearly seen in the winter-buds of shrubs and trees, in 

 consequence of the periodical arrest of the growth of the shoot. 



\ 



FIG. 9. Diagrammatic longitudinal section 

 through the growing-point of a stem ; 6, the 

 leaves ; fcn, their axillary buds ; e, epidermis ; /, 

 fibrovascular bundles ; r, the cortex ; pi, plerome ; 

 m, pith. 



