STEMS OF MONOCOTYLEDONS AND DICOTYLEDONS. 129 



the centre of the stem, and that the hard and thick vascular 

 bundles, situated at the periphery of the stem, are older than 

 the softer ones occupying the centre. For stems like those of 

 Palms he used the term endogenous, giving the name exogenous 

 to the other class, in which new layers are added to the outside 

 of the wood. The terms endogenous and exogenous were 

 adopted by De Candolle, and have pla3'ed an important part 

 in Systematic Botany. Comparative researches have shown that 

 the term endogenous as applied to the growth of stems like 

 those of Palms is not appropriate, and hence the correlative 

 words have been generally 

 abandoned as names of the 

 two great groups of plants. 

 They are now generally re- 

 placed by the words monocoty- 

 ledonous and dicotyledonous 

 (see Vol. I. p. 69). 



Moreover, it is now gener- 

 ally admitted that, although 

 the distinctions pointed out in 

 366 namely, those relating 

 to the arrangement and course 

 of the bundles are valid for 

 most plants of the two great 

 groups, monocotyledons and 

 dicot3'ledons, thej'do not hold 

 for all. 



380. Instead of describing 

 the numerous exceptions to 

 both of these groups as ex- 

 ceptions, many authors have 

 endeavored to construct some 

 new classification which shall 

 embrace most of the anoma- 

 lies in one or more co-ordinate divisions. Of these attempted 



tendrils is resumed. Every leaf has five fibro- vascular bundles, which are 

 arranged unsvirmietrically, as shown in the fisiure. The long distance through 

 which some bundles can run before uniting with any others, and the differences 

 in structure at the successive nodes, are clearly exhibited in the diagram. 



FIG. 105. Diagrammatic projection of the disposition of the fibro-vascniar buwlles in 

 Phaseolus vulgaris. This diagram, like Fig. 104, supposes two longitudinal sections, 

 both seen from the :i xio : a, b,c,tl ; f. ft, h, i: >,m,n,o; q,r,x,t; w, r , w, x ; the succes- 

 sive leaf-traces, each with four fascicles. Of the upper leaf-trace, the first two fascicles, 

 y, z, are visible, e, k, k, p, fascicles for the three leaves below. Nageli.) 

 9 



