68 



ENDOGENOUS OK MONOCOTYLEDONOUS STEM, 



comes so hard as to witlistajid the blow of a hatchet. It has been 

 already stated that in the exogenous stem provision is made for 

 unlimited extension laterally, by the development of bundles of woody 

 fibres and vessels indefinitely, and the formation of a separable bark 

 which can be distended ; but in the endogenous stem there is no such 

 provision. Hence, when the first formed or lowest part of the stem 

 has increased to a certain amount, its progress is stopped by the hard 

 indistensible outer fibrous covering ; and the same thing takes place 

 successively in the higher parts of the stem, till at length all have ac- 

 quired a comparatively uniform size, as is seen in the coco-nut palm 

 (fig. 134, 1). In consequence of the small lateral increase of Palm- 

 stems, a woody twining plant does less injury to them than to trees 

 of exogenous growth. 



The growth of endogenous stems may be said to resemble an 

 ^ upward growth of an Exogen by 



terminal buds only, for there 

 is no cambium layer, and no 

 peripherical increase. In Palms, 

 whUe the terminal shoot is 

 developed, there are no an- 

 nual rings. The hardening of 

 the stem depends, in all pro- 

 bability, partly on internal 

 changes in the bast fibres, 

 similar to what takes place in 

 the heart-wood of Exogens. 

 Occasionally, at the upper part 

 of a palm-stem, there is an ap- 

 pearance of zones, but it does 

 not continue throughout the 

 stem. From the absence of 

 concentric circles, the age of a 

 Palm cannot be estimated in 

 the same way as that of an exo- 

 genous tree. The elongation, 

 however, of each species of 

 —-^ «.;- Palm is pretty regular, and by 



-■- --i:^^ j^ some idea may be formed 



^'s- 134- of its age. The rings on the 



stem do not usually indicate yearly growth. 



Fig. 134. Two endogenous or monoeotyledonous trees, belonging to different fami- 

 lies. 1. Cocos nucifera, or coco-nut, belonging to the Palm family. 2. Fandanus odora- 

 tissimus, or screw-pine, belonging to Pandanacese. The first has a simple unbranohed 

 stem, with a cluster of leaves at the summit ; the second has a branched stem, with nume- 

 rous leafy clusters, and peculiar aerial roots, proceeding from different parts of the stem. 

 Two Sgoies are given to indicate the height of the trees. 



