at Yn = 
Ney 
_. The structure of the wood of Dicotyledons agrees in its 
main features with that of Gymnosperms (see p. 333), a class 
of a generally lower type of organisation. ‘The main dis- 
tinction lies in the structure of the individual vascular 
bundles. In Gymnosperms there are in general no true 
II. 
Fic. 477 I1.—Transverse_ section through an older root of Ranunculus aces: G 
vessels formed centripetally ; Gc’ young vessels formed centrifugally ; BB bast- 
bundles ; s vascular bundle-sheath (x 200). | 
vessels; rows of vascular cells, which occur only in the medul- 
lary sheath, taking their place, and even then manifesting 
only a spiral or reticulate thickening (Fig. 478). The small 
exotic order of Gnetaceze furnishes an exception, the whole 
BB2 
se Special Morphology ‘and Classification. a7 TG 
