Anatomy of Solenostelic Ferns. 725 
quently repeated, although more or less imperfectly, in the 
development of its lateral shoots. 
In Davallia gibber osa two separate vascular strands run out 
from the stem into each lateral shoot, and the structure at the 
base of the shoot is similar to that described on page 695 as 
the simplest form of dorsiventral dictyostely. The lateral 
shoots are very numerous, but only a few of them ever become 
properly developed ; all the others remain abortive and form 
no visible projection upon the surface of the stem. These 
suppressed shoots, however, are still utilized for the purpose of 
bearing the roots. A number of these arise upon the lower 
or ventral meristele of the shoot, which now functions merely 
as a special radiciferous strand. 
I am inclined to believe that the radiciferous strands 
described by Trecul 1 and Lachmann 2 in Blechnnm braziliense , 
Scolopendrium officinale , D.C., Asplenium Serra , and others, 
should also be regarded as the vascular vestiges of suppressed 
lateral shoots. In the first two examples they consist, accord- 
ing to Lachmann, of a single solid vascular strand, but in 
Asplenium Serra , Trecul describes them as cylindrical vascular 
tubes. It has just been shown above that there are a number 
of Ferns the lateral shoots of which, if arrested at the right 
stage of their development, would present both these kinds of 
structure. 
In all the Polypodiaceae that I examined the xylem-strand 
of the true root-stele was invariably diarch. Its long axis 
was generally tangential to a radius of the stem in the trans- 
verse plane, but it was so often oblique, or even parallel to it, 
that this distinction is evidently of no great value. In their 
course through the cortex of the stem the root-steles some- 
times run directly outwards, more often they run obliquely 
forwards, or they may even take a zigzag course, running 
first of all towards the apex and then turning abruptly back- 
wards before reaching the surface of the stem, as in Dicksonia 
1 Remarques sur la position des trachees dans les Fougeres, 1 . c., p. 228. 
2 Contributions a l’histoire naturelle de la racine des Fougeres. Thesis pr^sent^e 
a la faculte des Sciences de Paris, Ser. A, No. n6, p. 102, 1889. 
