88 



OKGANOGRAPHY. 



after that period has arrived do them no injury, frequently not 

 even producing the slightest swelling on their surface; thus 

 proving incontestahly that such stems do not increase in diameter 

 after a certain age. The effect of such climbers is well seen in 

 fig. 176. If we compare this figure with that of an exogenous 

 stem {fig. 175), with a woody twining plant encircling it, we 

 find a striking difference ; for here we observe extensive swellings 

 produced, which exhibit a corresponding in- 

 Fig. 175. Fig, 176. crease of the diameter of the stem. Such a 

 comparison shows, in a very striking and 

 conclusive manner, the characteristic pecu- 

 liarities of the growth of exogenous and en- 

 dogenous stems. 



In Palms, as we have seen, (fig. 170, 1), 

 and commonly in other monocotyledonous 

 plants, there are no branches, the stems of 

 such plants having no power of forming 

 lateral buds, from which, as will be presently 

 noticed, branches can alone be produced. 

 These plants therefore grow simply by the 

 development of a terminal bud, which when 

 it unfolds crowns the summit with a tuft of 

 Dicotyiedo- foliage. Endogenous stems are therefore in 

 this respect exposed throughout their whole 

 around it. lengt-h to, as far as possible, the same influ- 



SoJ^stenneiuTiSed ^"^^^ as regards their increase in diameter, 

 by a woody twiner. and we find accordingly, that, as a rule, such 

 stems are almost uniformly cylindrical from 

 below upwards, being of the same diameter throughout (fig. 170). 

 In such a plant the destruction of the terminal bud necessarily 

 leads to its death, as it is then deprived of all mode of further 

 increase. In some endogenous trees, however, more than one bud 

 is developed: thus in the Doum Palm of Egypt (Hyphane the- 

 haica), two buds are formed, so that the stem is forked above {fig. 

 177) ; each branch again developes two other buds at its apex in 

 like manner, and this mode of growth is continued with the 

 successive branches, which are therefore also forked. In other 

 monocotyledonous plants we have lateral buds formed as in those 

 of exogenous growth ; thus this is the case in the Asparagus, in 

 the Screw Pine {fig. 170, 2), in the Dracaenas {fig. 178), &c. As 

 the lower part of such stems receives more vascular bundles 

 than the upper they are necessarily larger in their diameter at 

 that part, and thus these stems are conical or taper upwards like 

 those of dicotyledonous plants. 



Some endogenous stems present an anomalous structure ; thus 

 in most Grasses the stem is hollow {fig. 179, a), except at the 

 points where the leaves arise, at which parts solid partitions, 6, 

 are formed across the cavity, by which it is divided into a number 



Fig. 175. 



uous stem, with 

 woody twining plant 



