170 
WRIGHT : OBSERVATIONS ON 
adventitious root, and tapers off regularly towards the root 
apex. It is further* suggested that this difference may be a 
character of the species. 
The almost unlimited supply of material of D. reflexa 
allowed an investigation into this point. In the first place, 
an examination of the roots of young plants showed that 
cambial activity occurred at the base of the primary root 
and existed in no other part of the root system, though a 
considerable number of branches were given off. Exami- 
nation of another specimen consisting of a main root 3*5 
mm. in diameter and giving off a rootlet 2*0 mm. diameter 
revealed a pericyclic cambium in the older part of the main 
root, but which disappeared 1 cm. before rootlet insertion 
was reached. From this area to the root insertion, at and 
below the root insertion, no vascular cambium either 
pericyclic or cortical was present. Other specimens show- 
ing active cambium in all parts did not present any bulky 
secondary products at the root insertion. Even if the 
secondary products are present in maximum quantities at 
the root insertion, does it necessarily indicate the point of 
origin of the cambium from this area ? In studying the 
origin of the cambium it should be remembered that there 
is often a radial disposition of the cortical parenchyma, 
which in the presence of cambium might give rise to 
misleading notions. 
Nevertheless, when one reflects over the fact that each 
rootlet subsequently becomes the main root of another 
system, there seems every reason to expect that the differen- 
tiation of a cambium will start as in the primary and main 
roots from the base, 1^., point of insertion. The cases 
mentioned above can be explained on the grounds that the 
cambial activity, commencing at the base of the primary or 
main root, had spread so quickly that the areas of insertion 
of several rootlets were affected prior to the appearance of 
their own cambia. Whenever the differentiation of cam- 
bium in a rootlet is on any account delayed, it is obvious 
that that of the main root might easily overtake it. Further, 
