14 
Proceedings of the Boyal Society of Edinburgh. [Sess. 
from the cortex through the tube to the inner pith, giving ready com- 
munication by intercellular spaces, and by continuous tracts of living cells 
between the cortex and the pith. 
But the lips of the gap are en- 
tirely sheathed by endodermis, 
so that the barrier between 
vascular and non-vascular tissue 
is maintained intact: and it is 
continued without any leak or 
imperfection to the base of the 
plant. The passage from the 
protostele to the solenostele in 
the individual plant is marked 
Fig. 10 . — Histiopteris incisa (Thunbg.) J. Sm. Trans- by a great increase of the trans- 
verse section of internode .of rhizome ( x 10) show- verse sec ti 0 n of the stele (fig. 
mg corrugation oi solenostele. (Gwynne- Vaughan v ° 
collection, slide 1163, by Tansley.) 11). Clearly the proportion of 
Fig. 11. — Series of transverse sections of the stem of Pcesia podophylla, all drawn 
to the same scale, showing the great increase of stelar complexity as the 
conical stem expands upwards. ( X 4.) 
surface to bulk of the stele is greatly increased by the tubular form. 
But sometimes a still further increase is secured by corrugation of the tube, 
as in Histiopteris incisa (fig. 10). A still more remarkable way in which 
