24 



MOKPHOLOGT, OR COMPARATIVE ANATOMY. 



Fig. 15. 



(fig. 17), where the inner scales bear a green blade standing out free at 

 the top of the bulb, and again in various subaquatic Grasses with 

 creeping stems, in which the lower parts of the annual shoots often exhibit 

 large open sheaths with small rudiments of blade at their summits. The 

 region bearing perfect leaves forms the principal part of the axis in arbo- 

 rescent plants, where the leaf-scale region occur,* only at the points where 

 the protecting scales of the autumn buds are produced. The scars of the 

 leaf-series, crowded together from the non -development of the internodes, 

 are very visible at the base of the yearly shoots of many trees, for ex- 

 ample, of the Horse-chestnut : other trees reproduce, as it were, their 

 cotyledons at these points; the Jasmine, for example, exhibits a pair of 

 broad undivided leaves near the base of each annual shoot. In annual 

 plants the leaf-region is predominant, but the bract- 

 region is relatively more developed than in trees ; 

 and the same holds good of perennial herbaceous 

 plants. In arborescent plants the bract-region usually 

 does not present itself until the leaf-regions of many 

 years have been formed, and even then it is generally 

 formed from branches of the axis which have a sub- 

 ordinate share in giving the special form to the entire 

 plant : sometimes, however, the form of the ramifica- 

 tion is much affected by the position of this region, as 

 in the Horse-chestnut, Lilac, and other trees, where 

 the terminal buds of shoots are developed into an in- 

 florescence, which of course puts a stop to the onward 

 growth at these points. 



Leaf-scale Region. The leaf-scaled stem, 

 found especially among herbaceous perennial plants, 

 or such as live for several years without forming 

 a permanent woody stem above ground, is seldom 

 continuous with an axial root ; on the other hand, 

 it is very prone to produce adventitious roots, as 

 is natural to its usually subterranean or creep- Diagram of a plant O f 

 ing mode of growth. When its internodes are Q*7' f "*"' 



11 i j i t i i 1 1 ~t i T ^ AiiG leai-scaie, true- 



11 i j i t i i 1 1 ~t i T ^ , 



regularly although slightly developed year atter leaf, and bract regions 

 year, it forms an abbreviated stem, horizontal or SThlSme S. ente 

 ascending, either below or above ground. If the 

 main axis persists, producing a few branches each year, and as 

 it grows at one end slowly dies away at the other, a more or 

 less root-like structure is produced, termed a root-stock or rhizome 

 (fig. 12). If the growth of each axis decays away at regular in- 

 tervals, so as to isolate the products of the succeeding axes, the 

 result is different, and, instead of a branching rhizome, the axis 

 resolves itself into a number of detached portions, in the form of 

 corms. If these detached portions are chiefly composed of leaf- 

 scales, with the undeveloped stem small, so that they represent 

 enlarged buds, they are called bulbs (figs. 16 & 17). Another re- 



