Reed.—On the Anatomy of some Tubers. 541 
on to such an extent that the wood elements are now seen to be cut 
longitudinally even in a transverse section (Diagram I, Fig. 4 ). 
This derangement of the vascular tissue is a direct result of the 
tuberization of the stolon, and is brought about in the following manner:— 
Just about the region where the stolon joins on to the tuber it will be 
noticed (PI. XLII, Fig. 4 ) that the pith cells are becoming meristematic. 
Transverse sections a little farther in the tuber show that almost every cell 
of the pith is dividing. As a result of the activity of these pith cells a very 
considerable amount of parenchymatous tissue is added to the pith. It is 
this increase of medullary tissue which is responsible for the deranging 
of the vascular tissue. As the medullary cells continue their divisions they 
produce what is essentially a wedge of tissue which forces the xylem 
elements out of their normally vertical course and compels them to pursue 
a more or less oblique course. 
Diagram II shows the effect 
of the meristematic medulla 
on the strands of xylem. 
It must be fairly obvious 
that the large increase in 
quantity of the pith elements, 
and the consequent dilatation 
of the stolon to form a tuber, 
would under ordinary cir¬ 
cumstances also result in a 
rupture of the cortex, so 
that pari passu there is a 
7 . . . sL, stolon. 7’., tuber. M.Ph., medullary phloem. Longi- 
correspondmg division in the tndinal section of tuber at junction with stolon. 
cells of the cortex. 
It is thus seen that the pith contributes a very large portion to the 
tuberous tissue of the tuber. 
It now remains to trace the distribution of the medullary phloem 
in the tuber. 
The medullary phloem consists of the usual elements, sieve tubes, com¬ 
panion cells, and phloem parenchyma (PI. XLII, Figs. 1 and 2 ). 
At the time when the medullary cells of the stolon begin to become 
meristematic it is seen that the parenchyma cells between the protoxylem 
of the bundle and the medullary phloem also commence to divide. Simul¬ 
taneous with this the phloem parenchyma of the medullary phloem begins 
to divide. As a result of these divisions it is found that the medullary 
phloem becomes broken up into a large number of small strands isolated 
from each other by pockets of parenchyma (PL XLII, Fig. 2 , and 
Diagram II, M.Ph). 
The phloem strands which are distributed amongst the medullary 
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