Farmer —On the Structure of a Hybrid Fern. 535 
P. vulgare parentage was most strongly pronounced. The 
differences, inter se, of these reverted fronds is, I conceive, 
one of special interest, as affording a striking illustration 
of the unstable character of the hybrid. 
Turning to the internal structure of the stem and of the 
petiole, we find a close approximation, though not a complete 
resemblance, between P. Schneideri and P. dureum . 
The rhizome is almost exactly alike in the two cases, if 
one makes due allowance for a certain disparity of size. In 
both forms the vascular system is more complex, and the 
steles are larger than are those in P. elegan tissimum. 
In the leaf-stalk of P. Schneideri the preponderance of 
auremk characters is clearly marked, though in a less degree 
than in the rhizome. Thus an average-sized frond of P. aureum 
was found to possess, at the base of the stalk, two large 
steles beneath the adaxial face, together with four or five 
small ones, the whole group being disposed in a circle, as is 
shown in PI. XXIII, Figs. 1, 2, 3. The number of the small 
steles varies irregularly at different heights of the petiole, 
owing to the frequent anastomoses and repeated divarications 
which occur amongst them. On the other hand, the course 
of the two large adaxial steles is very regular. They run in 
a nearly parallel direction up the leaf-stalk, only fusing 
at a short distance below the region of the lamina. As 
regards P. elegan tissimum, the petiole possesses a far less 
complex vascular system. At the base, two large adaxial 
steles can be seen, accompanied usually by one but some- 
times by two very much attenuated strands, corresponding 
to the four or five subsidiary steles of P. aureum . At a very 
short distance up the stalk, however, the two larger strands 
can alone be seen, and these fuse together about half- 
way up the petiole (PI. XXIII, Fig. 5). An inspection of 
Figs. 1-8 on Plate XXIII will serve better than a 
description to illustrate the much greater approximation of 
P . Schneideri to P. aureum, as regards its vascular system, 
than to its other parent. The two large steles fuse rather 
earlier in the hybrid, and the number of the subsidiary 
