EXOGENS AND ENDOGENS. 77 
Indica), and the black Mangrove ( Rhizophora mangle) are men- 
tioned as examples of this singular conformation. 
a. The former originally arises with a single trunk. From the principal 
branches, when they have become so widely extended as to need additional sup- 
port, long, leafless shoots are sent down. When these shoots reach the earth, 
they take root, and become. new trunks, in all respects similar to the first. The 
branches thus supported still continue to advance, and other trunks to descend, 
until a single tree becomes a grove or forest. There is, in Hindostan, a tree of 
this kind, called the Banyan, which is said by travellers to stand upon more than 
3000 trunks, and to cover an area of 7 acres. The Mangrove tree is a native of 
the West Indies. ‘The new trunks of this tree are said to be formed from the 
seeds which germinate without becoming detached from the branches, sending 
down remarkably long, tapering radicles to the earth. 
§1. OF THE PHYSIOLOGICAL STRUCTURE OF THE EXOGENOUS STEM. 
194. The substance of herbaceous stems is soft and succu- 
lent, consisting almost wholly of cellular tissue, traversed longi- 
tudinally by some few bundles (strings) of woody fibre and 
vascular tissue, which diverge from the main stem into the 
leaves. 
195. This is essentially the structure of the first year’s growth 
of perennial plants also. Cellular tissue constitutes the frame- 
work of the yearly shoots of the oak, as well as of the annual 
pea, but in the former it becomes strengthened and consolidated 
by the deposition of ligneous fibre in subsequent years. 
a. Plants differ in respect to the arrangement of these fibres and vessels, and in 
the mode of their increase; on this difference is based that first grand distinction 
of Phznogamous plants into Exogens and Endogens, to which allusion has 
already been made (126—7). 
“196. The division of Exocrns (outside growers) includes all 
the trees and most of the herbaceous plants of temperate cli- 
mates, and is so named because the additions to the diameter 
of the stem are made ezternaily to the part already formed. 
197. The division of Enpocens (inside growers), including 
the grasses, and most bulbous. plants of temperate regions, and 
the palms, canes, &c. of the tropics, is named from the accre- 
tions of the stem being made within the portions already 
formed. 
198. In the exogenous structure, the stem consists of the pith, 
wood, and bark. 
