INTRODUCTION. 
5 
The Scales so visible upon some species have been thought merely an 
excrescent growth caused by superabundant sap exuding from the surcharged 
pores. Sprengel supposed that they were part of the epidermis itself, lacerated 
by the pressure of the juices beneath. Perhaps both of these opinions are 
correct, a part of the epidermis of the frond being first detached, and after- 
wards nourished in the same manner as animal hair, and although void of life 
yet increasing from the base. 
The Cuticle of the leafy portion of the frond presents a reticulated ap- 
pearance, the meshes having wavy sides, and is furnished on the under surface 
with respiratory stomata, similar in form and function to those of Flowering 
Plants. The number of these on a given space is in a great degree accordant 
with the rapidity of the frond’s withering when gathered. They are very abun- 
dant in Aspidium filix-foemina, Aspidium dilatatum, and Polypodium Dryop- 
teris. Thus is explained the reason for the drooping habit of this last and 
some other species. Be it observed, however, that in Grammitis Ceterachand 
Aspidium lobatum they are still more numerous, yet these latter plants do not 
wither so soon, a circumstance that may easily be accounted for from the frond 
being more entire in one, and thicker in both, the deprivation of an equal 
quantity of water not producing so great an effect. 
THE REPRODUCTION of Ferns is a subject involved in much obscurity. 
Hcdwig, Bernliardi, and others have proposed theories to explain this intricate 
matter, but without success. That the Ferns have no visible flowers is evi- 
dent, but that they have some apparatus analogous to stamens and anthers, is 
maintained by most of our first Botanists. This opinion has apparently been 
adopted merely to get rid of the doctrine of spontaneous impregnation, which, 
however unsatisfactory, must not wholly be discarded until something more 
plausible be substituted. At present nothing whatever has been discovered of 
the origin of the germinating principle in any of the Cryptogamic orders ; nor 
the laws which regulate the formation and development of their spores. As 
regards our present tribe, so keen has been the search, that every part of the 
plant has been subjected to the minutest investigation : not only the thecae, their 
ring, and their cover, but the spiral vessels of the rachis, the stomata upon their 
cuticle, and the glands which are sometimes found attending upon them. 
Seeds or Spores. — The small, round, rough grains contained in the tliecac, 
considered formerly as gemmae or buds, are now known as seeds, but differing 
from common seeds in many respects. They have no cotyledons, but are a 
mass of cellular substance. Instead of sending upwards a plumule, and down- 
wards a radical, from fixed points, they grow indifferently from any part of their 
surface, that most exposed to light shooting into the future frond, while the 
deeper point propels the root. Owing to these differences the seeds have been 
called, not only here but in all the tribes of Cryptogamic vegetables, spores 
