174 



MORPHOLOGY OF MEMBERS, 



endogenous origin (Fig. 128, K}C)\ they are developed out of a cell in the interior of 

 the tissue of the stem near to the growing point, and afterwards break through the base 

 of the older leaf-sheaths. In some Jungermanniese the normal terminal branching of 

 the stem takes place partially or entirely by endogenous formation of shoots ^ 



With these exceptions all normal lateral branches produced at the cone of growth 

 of the bud or in its neighbourhood are, like the leaves, exogenous. 



(f) The lateral branches which arise normally below the growing apex of a mother- 

 shoot are always produced in acropetal order, like the leaves, with which they exhibit 

 various relationships as to position, age, and number. 



(n) The numerical relationship of the lateral branches to the leaves formed ou 

 the same axis is variable. If the number is unequal, a greater number of leaves; 

 than of branchlets usually arises on the same axis; in Muscineae, Ferns, Rhizocarpeae. 

 Cycadeae, and Coaiferae a much larger number, A branchlet may arise when a de- 

 finite number of leaves has been formed, as in many Muscineae and some Ferns, or 



Fig. 129. — Longitudinal section through the apical 

 region of a branch of Cletnatis apiifoUa; s apex of the 

 stem ; b b leaves ; ^^ the first traces of spiral vessels, 

 bending out uninterruptedly from the stem into the leaves. 



FIG. i:-,o.-'^n\h of Muscari botryoides ; one of the 

 lower bulb-scales is thrown back, in order to show the 

 numerous buds standing side by side in its axil. 



the formation of a branchlet results when the increase in length of the primary axis 

 and the formation of its leaves ceases for a time and is subsequently renewed, as 

 in Abies. When the leaves stand in whorls, the number of the lateral branches 

 may be equal to that of the members of the whorl, as in Equisetaceae, or smaller, as 

 in Characeae. It is unusual for the number of branchlets to be larger than that of 

 the leaves, but this occurs in some Angiosperms, where two or more lateral buds often 

 arise side by side above a leaf (Fig. 130), or one above another, as in Aristolochia Sipho, 

 Gleditschia, &c. In most Angiosperms the number of the lateral branchlets (with the 

 exception of the flower-shoots) is, at first, the same as that of the leaves ; but usually 

 only a much smaller number continue to develope. 



(/3) The relationship in position and origin of leaves and branches is constant in each 

 species and often in a whole cla.ss of plants. The lateral branches arise below the leaves 

 (according to the acute investigations of Leitgeb 2) probably in all Mosses, as well as in 



» [See Leitgeb, Bot. Zeit., 1R72.] 



^ Leitgeb, Beitrage zur Entwickelungsgeschichte der Pflanzenorgane, in Sitzungsber. der kaij 



