Farmer. — On the Structure of a Hybrid Fern . 543 
condition of our knowledge we can only grope about after 
a clue to the solution of the problems before us — a clue 
which recent cytological work seems to have shown us to 
be less accessible than we had previously hoped. But I do 
not believe they are really unsoluble ; they demand, however, 
experimental treatment on the part of botanists such as they 
have already begun to receive at the hands of comparative 
physiologists, and it behoves cytologists not to neglect such 
means of assistance as a careful study of the structure and 
origin of hybrids, in the garden as well 3s in the laboratory, 
is able to provide. 
EXPLANATION OF FIGURES IN PLATES 
XXIII AND XXIV. 
Illustrating Professor Farmer’s paper on the Structure of a Hybrid Fern. 
[Figs. 1— 1 3, camera lucida drawings, Zeiss A x 2 oc. (the figures 1-9 reduced to 
£). Figs. 14-19, photographs, ] natural size.] 
Figs. 1, 2, 3. Sections of the petiole of Polypodium aureum. 
Fig. i. Transverse section through the base of the petiole, showing peripheral 
band of sclerenchyma, scl., and the steles, two large and five small ones. e. endo- 
dermis ; P. pericycle ; ph. phloem ; xy. xylem. 
Fig. 2. Section a little below the middle of the petiole. Shows anastomosis 
between the smaller steles. 
Fig. 3. Section a little below the region of the lamina of the leaf. 
Fig. 4. Section through the base of the petiole of Polypodiwn vulgare , var. 
elegantissimum. 
Fig. 5. Section taken through the same petiole at i the distance between the 
base and the insertion of the lowest pinna. 
Figs. 6, 7, 8. Sections through the petiole of Polypodium Schneideri , taken from 
regions corresponding with those of P. aureum in Figs. 1-3. 
Fig. 9. Epidermis from the lower surface of the leaf of Polypodium aureum. 
Fig. 10. Epidermis from the lower surface of the leaf of P. vulgare , var. 
elegantissun u m . 
Fig. 11. Epidermis from the lower surface of the leaf of P. Schneideri. 
Fig. 12. Sporangium (showing barren contents) from dissected frond of 
P. Schneideri. 
