- TrpoucHINA MoriCANDIANA, BAILL. 247 
2. The branch rootlets which arise, as is shown in Figs. 3 and 
7, as lateral out-growths from the club-shaped extremity of the 
root. 
Both phenomena are a consequence of the death of the tip of 
the mother root, which brings about an area of dead tissue in 
the centre of the end of the root. Around this dead tissue an 
inner cambium is formed in the pith (Fig. 13 zc.), and as the 
root tissues continue growth to form the swollen end of the root, 
this inner cambium keeps pace in the formation of tissue as a 
lining to the central cavity thus produced in the root (Fig. 14 zc.). 
The ultimate destiny of this inner cambium is the point to which 
I have now to direct special attention. 
It will simplify description if we base this upon the case where 
the mother root splits into two flattened lobes. An examination 
of one of these lobes when completely formed shows a structure 
such as is represented in Fig. 21. That is to say, there is similar 
construction to that of the mother root, save that the whole organ, 
instead of being cylindric (Figs. 11, 12), is compressed and 
bilateral. There is a pith, a vascular ring with wood cambium, 
a cortex, and cork cambium. We have therefore in the case in 
point two root-organs with complete though compressed root 
structure, which have arisen by the splitting of one complete 
cylindric one. How does this come about? 
Briefly—the inner cambium (Figs. 13, 14 zc) is the tissue 
through which the half vascular system in each of the lobes 
formed by the splitting of the mother root is completed as a 
ring. Reference to Fig. 10 will make clear the process, and 
transition stages are shown in Figs. 18, 19, 20. 
When the tip of the cylindric mother root dies and the root 
splits, each half has necessarily on its outer convex side half of 
the cortex of the mother root covering a half of the vascular 
cylinder, within which lies a part of the pith with a layer of inner 
cambium and a portion of the cells that have so far been formed 
by it. Each half-root is then dorsiventral. The inner cambium 
now develops tissue rapidly to complete the vascular cylinder, 
and it is clear that in order to do this the cambial cells formed 
on the originally inner side of this inner cambium will be phleem 
elements, those on the originally outer side will be xlyem ele- 
ments. From this inner cambium the cortex required to complete 
that of the half-root is also derived, and in it the subsequent cork 
cambium arises, 
