DRACÆNA REFLEXA. 
171 
the formation of the rootlet may itself be delayed until 
cambial activity has spread from the base of the main root 
to the area from which the rootlet subsequently emerges. 
It would therefore seem most likely that in order to obtain 
specimens showing the commencement of cambium at the 
insertion of the rootlets material should be examined in 
which the primary root is relatively young, and which, 
nevertheless, bears rootlets in a comparatively advanced 
condition of development. 
These conditions obtained in one specimen consisting of 
an adventitious young root 3*2 mm. diameter, bearing a 
rootlet 50 mm. from its apex. The rootlet was compara- 
tively well developed, being 60 mm. long, and therefore 
extending beyond the apex of the main root on which it was 
inserted. An examination of the area of insertion showed 
the commencement of a pericyclic cambium on the side of 
the insertion which extended to less than 1 millimetre 
above the insertion and to a greater distance below, the 
insertion. Here, then, was a case in which cambium 
appeared independently at the insertion of the rootlet, first 
being purely pericyclic, and subsequently, after a scattering 
of the lignified endodermis, continued by the inner cells of 
the cortex. 
It would therefore appear that either of the contentions 
held by Strasburger and Scott and Brebner may be valid 
according to the vitality of the cambium in the main roots, 
or the delayed or enhanced development of lateral rootlets 
in the particular system dealt with. Though many speci- 
mens were examined, the details observed were not such as 
to allow one to conclude that the area of insertion of a 
branch root was the centre from which the differentiation 
of the cambium for the main roots proceeded. The develop- 
ment of the cambium at the insertion point was more the 
starting point for the rootlet itself and not for the mother 
root, and in this respect would seem to differ from what 
prevails in D. Draco and D, fragrans. 
( 23 ) 
