MORPHOLOGY 



19 



The Origin of New Shoots. — The formation of new growing points 

 by the bifurcation of older points of growth, in a manner similar to that 

 already described for Dictyota dichotoma 

 (Fig. 8), occurs also, in almost typical form, 

 in the lower thalloid Hepaticae (Biecia 

 fluitans, Fig. 10). Among the Cormophytes 

 this method of producing new shoots is of 

 less frequent occurrence, and is then 

 mainly limited to the Pteridophytes, for 

 one division of which, the Lycopodiaceae, it 

 is characteristic. In this case, whenever a 

 shoot is in process of bifurcation, two new 

 vegetative cones are formed by the division 

 of the growing point (Fig. 18). In most 

 of the Lycopodiaceae the new shoots thus 

 formed develop unequally ; the weaker 

 becomes pushed to one side and ultimately 

 appears as a lateral branch (Fig. 19). 

 Although a relationship as regards posi- 

 tion is generally apparent between the 

 origin of leaves and the lateral shoots, in 

 the system of branching resulting from such 

 a bifurcation of the vegetative cone this 



Fig. 18. — Longitudinal section of a 

 bifurcating shoot (p) of Lyca- 

 podium alpiuum, showing un- 

 equal development of the rudi- 

 mentary shoots, p', p" ; o, leaf 

 rudiments ; c, cortex ; /, vascular 

 strands. (After Hegelmaier, 

 x 60.) 



connection does not exist. 

 In the more highly developed Bryophytes, particularly in the true 

 Mosses, new shoots arise obliquely below the 

 still rudimentary leaves at some distance from 

 the growing point. In the Phanerogams new 

 shoots generally arise in the axils of the leaves. 

 In the accompanying illustration of a longi- 

 tudinal section of a phanerogamic shoot (Fig. 

 17) the rudiment of a shoot (g) is just appear- 

 fig. 19.— Bifurcating shoot ing in the axil of the third uppermost leaf ; in 

 the axils of the next older leaves the conical 

 protuberances of the embryonic leaves are 

 already beginning to appear on the still rudi- 

 mentary shoot. These rudimentary shoots may 

 either continue to develop, or they may remain 

 for a time in an embryonic condition, as buds. Shoots thus pro- 

 duced in the axils of leaves are termed axillary SHOOTS. The leaf 

 in the axil of which a shoot develops is called its subtending leaf. 

 An axillary shoot is usually situated in a line with the middle of its 

 subtending leaf, although it sometimes becomes pushed to one side. 

 As a rule, only one shoot develops in the axil of a leaf, yet there are 

 instances where it is followed by additional or accessory shoots, which 

 •either stand over one another (serial buds), as in Lonicera, Gleditschia, 

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



(p) of Lycopodium inun- 

 dation, showing unequal 

 development of the rudi- 

 mentary shoots, p', p" ; 

 &, leaf rudiments. (After 

 Hegelmaier, x 40.) 



