222 PLANT ANATOMY. 
(Fig. 18079). In the case of dicotyledonous foliage trees, the 
distinction between autumn and spring wood is also further in 
creased by the fact that the latter is much richer in yessels.! 
(Fig. 78 jf). 
The so-called wood-ring of dicotyledonous stems is produced 
Fie. 139.—Libriform from Quassia wood. 
by the confluence of isolated vascular bundles, in their vascular 
as well as in their sieve portions, through the activity of an 
- (intrafascicular) cambium, the bundles being originally formed 
in a loose circle, 
1 Berg’s ‘‘ Atlas,” plate xxv., 60, and plate v., 21. 
