Bower.—Studies in the Phytogeny of the Filicales. VIL 19 
from time to time by giving off ‘ compensation-strands \ By means of these 
it is connected to the anterior margin of each foliar gap in the outer ring. 
The departure of each leaf-trace causes a gap also in the inner ring, which 
appears usually to be composed of two meristeles of unequal size. The 
origin of the compensation-strand is seen opposite to the upper foliar gap in 
Fig* I 7> f g- Its progress outwards is seen in Fig. 17, h , i, j ; and its 
entry into the foliar gap, which it thus closes, is shown in Fig. 17, £,/. 
Other illustrations of the process may be seen in the sections of this series* 
(X h c <£ 
Fig. 17. a-l. Series of transverse sections of the stem of Saccoloma elegans , in succession from 
below upwards. The numbers indicate the places of the actual sections drawn in the whole series 
cut. Natural size. 
The attachment of the compensation-strand is comparable to the less com¬ 
plicated case of Pteris elata described by Mettenius and depicted by 
Gwynne-Vaughan. 1 An occasional vascular boss appears on the outer sur¬ 
face of the inner ring (Fig. 17, b,.c, d), but it ends blindly, and does not 
establish connexion with the outer ring. Lastly, the central vascular tract 
is at times a single, rather thick strand (Fig. 17, a, b ), which establishes 
connexion with the inner vascular ring (Fig. 17, c , d , e) without dis¬ 
turbing it. But elsewhere considerable irregularities may accompany these 
fusions, as seen in Fig. 17 1 g—l* It thus appears that the inner system is 
1 1 . c., Fig. 14. 
