DIV. I 



MORPHOLOGY 



121 



or before the leaf has developed. In the latter case the leaf-rudiment arises from 

 the tissue to the lower side of the branch primordium (Fig. 142 I1JT). On the 



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FIG. 142. Diagrams of the developmental relations between the leaf primordium and the axillary 

 shoot. (After GOEBEL.) 



other hand, the branch may be formed from the young leaf primordium (Fig. 

 142 II}. Lastly, in dorsiventral shoots extra-axillary shoots may arise laterally 

 from the leaf primordia. 



In the longitudinal section of a growing point in Fig. 98 the 

 youngest rudiment of a lateral shoot (g) is already visible, projecting 

 in the axil of the uppermost leaf. In the axils of the following leaves 

 the branch primordia, since they arose in acropetal succession, are 

 larger and have begun to form their leaves. The shoots developed 

 from such AXILLARY BUDS are termed AXILLARY SHOOTS; the bud 

 which terminates the growing end of the main 

 shoot is termed, in contrast to the axillary 

 buds, a TERMINAL BUD. The leaf, in the axil 

 of which a bud stands, is its SUBTENDING LEAF 

 (Fig. 144 db). The plane passing through the 

 midrib of this leaf and the parent axis is the 

 MEDIAN PLANE of the leaf. Usually the axillary 

 bud is situated in the median plane of its sub- 

 tending leaf, but it may be displaced laterally. 

 It is the rule in Angiosperms that each foliage 

 leaf has a single axillary bud ; in some Gymno- 

 sperms, on the other hand, there is not an 

 axillary bud to every leaf. 



As a rule, only one shoot develops in the axil of 

 a leaf, yet there are instances where it is followed by FIG. 143. Samolus valerandi, 

 additional or ACCESSORY SHOOTS, which either stand over each axillary shoot (a) bear- 

 one another (serial buds), as in Lonicera, Gleditschia, in s its subte nding leaf (0, 

 Gymnocladus, or side by side (collateral buds), as in many 

 Liliaceae, e.g. species of Allium and Muscari. A 

 displacement from the position originally occupied by the members of a shoot 

 frequently results from intercalary growth. A bud may thus, for example, 

 become pushed out of the axil of its subtending leaf, and thus apparently have 

 its origin higher on the stem ; or a subtending leaf in the course of its growth may 

 carry its axillary bud along with it, so that the shoot which afterwards develops 



