174 COOK 



tral American rubber tree {Castillo) there are two kinds of 

 branches. The metamers composing one type of branches are 

 in all respects the equivalents of those of the primary stem or 

 trunk, while the others are distinctly inferior and unable to pro- 

 duce or regenerate primary branches. 



STRUCTURE OF VEGETATIVE METAMERS. 



The ideal of a vegetative metamer of an angiospermous plant 

 individual includes three kinds of parts : (i) the internode proper, 

 forming a section of the stem of the plant, (2) an expanded 

 assimilatory plate or leaf, usually adapted for exposure to light, 

 and (3) a terete absorptive organ, or root, w'hich usually buries 

 itself in the ground and there produces root-hairs. 



Internodes are generally simple, but the coffee shrub might 

 be said to have compound internodes, since each primary inter- 

 node produces two branches from extra-axillary buds. The 

 number of leaves borne by each internode is usually only one or 

 two, but some plants have whorls of several leaves, though this 

 condition may be reached by the shortening of some of the 

 joints. In most plants onl}^ the lower internodes produce roots, 

 but there are also many species, as among the aroids and figs, 

 where all the internodes bear roots freely, and in a very large 

 number of plants they have the power of doing so under special 

 conditions. 



The more primitive types of leaves consist of two parts, a 

 cylindrical basal sheath surrounding the next internode, and an 

 expanded terminal blade. From the basal sheath stipules have 

 been derived like those of Rosaceas and Ranunculaceas, and 

 bud-scales like those of Ficus and Castilla. In Inodcs, Thrinax 

 and other fan-palms the sheath has been prolonged into a peti- 

 ole, which ends in aligule. On the other hand, Dcsmoncus and 

 related genera of cocoid palms have ligules in the same position 

 as the grasses, as direct extensions of the sheath, above the in- 

 sertion of the blade. Evidence is thus afforded that in the 

 Cocaceas, at least, the petiole is not a part of the sheath, but a 

 prolonged naked base of the midrib of the blade. Similar dif- 

 ferences in the homologies of the petioles are doubtless to be 

 found in the leaves of other angiosperms. 



