28 



BOTANY 



PAKT I 



{GleiUischia) afford instructive examples. The thorns are simple or 

 hranched, hard, pointed bodies. In Gleditschia (Fig. 30) the thorns 

 are developed primarily from the uppermost of several serial buds ; 

 while secondary thorns may develop on older portions of the stem 

 from the lower buds of the series, and thus give rise to clusters of 

 thorns. In CoUetia cruciata all the shoots are flattened and spiny, so 

 that, in addition to serving as protective structures, they perform 

 the duties of the leaves, which are quickly lost. This plant is an 



American shrub belonging to the Rhamnaceae, 

 and grows in dry, sunny situations. 



Flowers. — The most marked changes in 

 the form of the shoots, due to the displace- 

 ment and union of their different members, 

 take place in phanerogamic flowers (Fig. 39). 

 The shoots from which flowers are developed 

 are termed floral shoots, in contrast to 

 the FOLIAGE SHOOTS, the 

 functions of which are 

 merely vegetative. The 

 axis of the floral shoot re- 

 mains short, and becomes 

 flattened or even depressed 

 at the tip. The leaves 

 which spring from the floral 

 axis often become united 

 with one another and with 

 the axis itself. In such 

 cases thorough investiga- 

 tion of the development 

 and the comparative mor- 

 phology of the flower is 

 necessary to reveal the 

 modifications which have 

 taken place during its evolution. In most instances the rule seems 

 to hold that axillary buds are not formed within a flower except in 

 cases of abnormal development. 



The Order of Sequence of Shoots. — If the vegetative cone of the 

 primary axis of a plant, after reaching maturity, is capable of repro- 

 duction, a plant with but one axis will result, and the plant is 

 designated UNIAXIAL or HAPLOCAULESCENT. Usually, however, it is 

 not until a plant has acquired axes of a second or third order, when it 

 is said to be diplocaulescent or trtplocaulescent, or of the nth 

 order, that the capacity for reproduction is attained. A good illus- 

 tration of a plant with a single axis is afforded by the Poppy, in 

 which the first shoot produced from the embryo terminates in a flower, 

 that is, in that organ of Phanerogams which includes the sexual 



Fio. 29. — Quinaria Veitchii. R, It, 

 Stem-tendrils. (J nat. size.) 



Fi(i. 30.— Stem-tliorn of 

 Gleditschia triaaiiithos. 

 (i nat. size.) 



