founded on the Structure of their Seedlings . 59 
which I have compared with each other agree in every detail. 
They are cut from three seedlings, of which A 6 , that outlined 
in Fig. 1 (PL VI), is the oldest, and A 2 , from which Figs. 
2-6 are drawn, is the youngest. The intermediate seedling 
A 5 is nearly as old as A 6 . The course of the bundles in 
the region intermediate between Fig. 5, PL VI and Fig. 1 on 
Pl. VII is indicated in B, Diagram X. The details of the 
process differ slightly in the three seedlings cut. 
In all three the traces keep to a zone which lies about half- 
way between the periphery and the centre of the tuber, and 
their course downwards follows its outline, first curving out- 
wards and then closing in again. The formation of a phloem 
girdle is suggested even in A 2 , and is indicated much more 
completely in the older seedlings A 5 and A 6 . The four 
groups of xylem internal to the phloem groups (Fig. 5) show 
a tendency to split into two or even three strands. In seed- 
ling A 2 one only of the four xylem bundles splits in this 
way — the lowest in Fig. 5. When the four protoxylem 
groups of the early root-stele are in course of construction, 
which is always much lower down in the tuber, we find in A 2 
that the xylem group in the lower left-hand corner of the 
section is being built up of three strands instead of two 
(Fig. 6). Moreover, an offshoot from the aberrant group 
of xylem has already ended blindly. 
The four corresponding xylem groups of seedlings A 5 and 
A 6 commonly split into two or more strands. To follow each 
minute cluster of xylem elements through a series of sections 
cut from a comparatively massive tuber is a task requiring 
some patience. I have done so in these three seedlings, and 
have convinced myself that the result may be fairly repre- 
sented by the generalized Figure B in Diagram X. The 
strands from each original group commonly unite again lower 
down : anastomoses with adjacent groups do occur, but are 
exceptional. The whole process is clearly an adaptation 
to the needs of the tuber. I suspected at first that a com- 
plete xylem network was indicated with which the first 
cauline roots would later be connected, but a series of sections 
