certain Species of the Genus Chris tisonia . 109 
cells. After the young root has emerged from the cortex 
of its parent and begins to grow rapidly in thickness nearly 
all traces of its endogenous origin become obliterated, indeed 
it is often very difficult to tell at the mature stage whether 
it is with a case of exogeny or endogeny that one has to deal ; 
it was only after careful scrutiny and the discovery in most, if 
not all, cases of a short flap of two or three layers of cortical 
cells (the evidence of rupture), that the typical endogenous 
origin of these root-branches was determined. In the develop- 
ment of a branch, the cortex of the parent-root often becomes 
very much bulged out, so that the flap just mentioned comes 
to lie at some distance along what appears at first sight to be 
the basal part of the lateral member itself. The place of 
origin of a rootlet, at the stage shown in Fig. 19, is indicated 
by minute swellings on the external surface of the root, caused 
by the raising of the cortex at those points. 
The stem , as has been stated above, arises from the root. 
It is of endogenous and probably also of peri cyclic origin. 
Like the lateral root, its origin becomes obscured as it 
advances in age, so that it gives the impression of arising 
from the second or third layer of the cortex, reckoning from 
the outside. An examination of Fig. 20, however, which is 
drawn from two sections of the root of C. subacaulis , Gardn., 
will reveal pretty plainly the real origin of this organ from 
the region of the central cylinder. It is a much broader out- 
growth than the young root, with a flatter and broader apex, 
which region is seen to be covered by the first two young 
leaves (/). Unlike the root, its sole mode of piercing the 
cortex is the mechanical one of pushing a path for itself 
through the surrounding cells. As the stem grows outward 
and finally bursts the outermost cortical layer, the successive 
young foliar organs are rapidly produced ; these give the 
rounded, knob-like character to the young stems as they 
appear scattered on the surface of the root When the young- 
stem has attained to about one-fourth of an inch in length it 
often gives rise to adventitious structures, which are roots and 
arise endogenously ; they grow down into the substratum. 
