TSrXOGEKS AND -ENDOGENS. 77 



Ihdica), and the black Ivlangrove {BJiizophora mangle) are inen- 

 tionecl as examples of tliis singular conformation.) 



a. Tlie former originally arises ;\\itli n single tn;nk. Froin the principal 

 1)ranches, when they have become so widely extended as to need additional sup- 

 port, long, leafless shoots are sent down, "^^lien these shoots reach the earth, 

 thev take root, and become new trunks, in all respects similar to tlie first. The 

 branches thus supported still continue to advance, and other tiimks to descend, 

 until a single tive becomes a grove or forest. There is, in Kindostan, a ti-ee of 

 this kind, called the Banyan, which is said by travellers to stand upon more than 

 3000 tiTinks, and to cover an area of 7 acres. The Mangrove tree is a native of 

 the "West Indies. The new tranks of this tree ar« said to be formed from the 

 «eed3 which gemiinate without becoming detached from the branches, sending 

 down remarkably long, tapering radicles to the earth, i 



f 1. OF THE PHYSIOLOGICAL STRUCTURE OF THE EXOGENOUS STEM. 



194. The substance of herbaceo?/s 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, Vvdiich diverge from the main stem into the 

 leaves. J 



19-5. This is essentially the stmcture of the Jirst year's growth 

 of perennial plants also. Cellular tissue/constitutes the frame- 

 work of the yearly shoots of the oak, as Vv^ell as of the annual 

 pea)but in the former it becomes strengthened and consolidated 

 .by the dej^wsition of ligneous fibre in subsequent years. 



a. Plants differ in respect to the arrangement of these fibres and vessels, and in 

 She mode of then- increase ; on this difference is based that first grand distinction 

 ■of Phamogamous plants into Exogens and Endogens, to which allusion .has 

 .already been made ( 126 — 7 ) . 



196. The division of Exogens (outside growers), includes all 

 the trees and most of the herbaceous plants of temperate ch- 

 mates, and is so named because the additions to the diameter 

 of the stem are made externally to the part already formed^ 



197. The division of Endogens (inside growers), including 

 (the grasses, and most bulbous pla.nts of temperate regions, and 



the palms, canes, &e. of the tropics, is named from the accre- 

 tions of th« stem being made ivithin the portions already 

 formed. 



198. Li the exogenous structure4-lhe stem consists of the pith, 

 ti'^ood, and bark: 



