ANATOMY OF TISSUES. 69 
Bast ) 
pagre Sieve-tubes | 
| Accompanying cells ee Fib 
Compound | one Cambiform ate 
Mestome 1 vascular 
or Hadrome ( Ducts Bund! 
| eae Ener n eases: 
eeee Xylem 
[ V aia: | Wood parenchyma 
Libriform 
According to this table the term mestome is used for that 
part of the bundle which has to do chiefly with nutrition ; this 
is subdivided into leptome or cribrose part, hadrome or vascular 
part. If all the elements of phloem and xylem are present, the 
leptome becomes phloem and the hadrome becomes xylem. Bast 
and libriform together are called stereome, or mechanical tissue, 
on the ground that their chief function is that of support. 
GROUND OR FUNDAMENTAL SYSTEM. 
In this system are included all the lasting cells not found 
in either the epidermal or vascular system. ‘They are derived 
from both plerome and periblem, their position, depending on 
the nature of the plant or organ in which they occur. For 
example, the arrangement of the vascular tissues differs in stem 
and root and there is therefore a corresponding difference in the 
position of the ground tissue. The cells of the latter are nearly 
isodiametric, and differ greatly in size. They are thin-walled, 
with frequent intercellular spaces, and in certain localities they 
often remain living and active during the lifetime of the plant. 
The lasting cells of the three systems just described origi- 
nate for the most part from the three primary meristems. That 
part of the vascular or fibrous system described as simple bundles 
forms an exception to this rule. Another exception is found 
in the phloem and xylem elements derived from those cambium 
cells which were not present in the original bundle. These 
cells, it will be remembered, originate by certain parenchymatic | 
