38 Bower.—Studies in the Phytogeny of the Filicales. VIL 
incidentally it may happen that two pockets are observed side by side in 
the same transverse section, and pursue for some distance an independent 
course, finally coalescing. They thus register structurally the independent 
effect of the insertion of the several leaves upon the central tissues of 
the stele. Soon an encroachment of vascular tissue from the inner surface of 
Fig. 27. i-iv. Vascular system of the young plant of Pteris fiodophylla, as seen in successive 
transverse sections at its base, (x 35.) 
Fig. 27 bis. v-viii. Similar sections of Pterispodophylla, showing a more advanced 
state, (x 5.) 
the solenostele appears. It projects into the pith from the side of the tube 
where the last leaf-trace was given off (Fig. 27, i); it is abstricted (ii), 
and takes an oblique course across the tube to a point almost opposite, 
where meanwhile the next leaf-trace has just been detached (iii). There 
it acts as a compensation-strand filling up the leaf-gap. But almost at once 
