of Dio scored prehensilis. 423 
development of which is centrifugal, are also multinucleate, as 
also are some of the larger sieve-tubes. 
It is doubtful whether these structures follow the same 
course of development as the central vessels. 
8. The vascular strands of the spine-bearing roots become 
very hard, the regions immediately external to the phloem- 
groups being the first to become lignifiedf* 
9. The large spines originate as thick lateral roots, and 
it is only at the extreme apex that a normal root-structure 
obtains. 
10. At the base of these thorns the phloem-groups are 
arranged in a circle at the periphery of the central cylinder ; 
as the apex is reached it is seen that the phloem-strands 
travel in an irregular manner throughout the whole area of 
the stele. Their course is sinuous, and they anastomose with 
one another ; at the extreme apex the phloem consists of but 
few strands arranged normally. 
This arrangement is probably to facilitate the extensive 
lignification of the spine. 
11. At the base of the thorn the xylem is chiefly restricted 
to two large peripheral masses just within the phloem-ring. 
Towards the apex the xylem is more evenly distributed, and 
gradually takes up a position nearer the centre of the stele. 
The Royal College of Science, 
South Kensington. 
