;4'-> VASCULAR CRYPTOGAMS. 



and that the upper part of the embryo between the apex of the stem and the base 

 of the root becomes transformed into a special organ, the Foot, by which the young 

 plant attaches itself to the tissue of the prothallium, in order to draw nourishment 

 from it, while the first roots and leaves are being put out. This foot or apparatus 

 for obtaining nourishment, which I consider a lateral structure, is called by Hofmeister 

 the first axis of growth, or primary axis of the Fern ; the leaf-bearing axis arises upon 

 it as a lateral shoot. But on this point also I consider, in opposition to the views 

 of this distinguished morphologist, that the analogy with the processes described by 

 Pringsheim in Salvinia must not be lost sight of; I must refer to the description of 

 the origin of the embryo in the archegonium given under the Rhizocarpese. 



The first parts of the stem and the roots and leaves, which are now developed 

 in succession from the embryo, are very small, and remain so ; those which are 

 formed later are gradually larger. The leaves become constantly more complex in 

 form, and the structure of the stem more intricate as the new additions to it increase 

 in diameter. The first parts of the stem, like the first leaf-stalks, contain each only 

 one axial fibro-vascular bundle ; the later ones a larger number. In this manner the 

 Fern continues to gain strength, not by subsequent increase of size of the embryonic 

 structures, but by each successive part attaining a more considerable size and 

 development than the preceding ones; until at length a kind of stationary con- 

 dition is arrived at in which the newly-formed organs are nearly similar to the 

 preceding ones. The following observations refer especially to this mature 

 condition of Ferns. 



The mature Fern is, in some Hymenophyllacese, a small delicate plant, not 

 much exceeding in dimensions the larger IMuscinese ; in other sections the fully 

 grown plants attain the size of considerable shrubs ; some species, natives of the 

 Tropics and of the Southern Hemisphere, assume even a palm-like habit, and are 

 called Tree-ferns. The stem creeps on or beneath the ground (as in Polypodium 

 and Pteris aquilijia), or climbs up rocks and stems; in some it ascends obliquely 

 {e.g. Aspidiiwi Filix-mas)\ in Tree-ferns it rises up vertically in the form of a 

 column. The roots are usually very numerous ; in Tree-ferns the stem is often 

 entirely covered by a dense mantle of them. They arise on the stem in acro- 

 petal succession ; sometimes close to the growing apex of the stem (as in Pteris 

 aquilind). When the internodes remain very short, and the stem is entirely covered 

 with the bases of the leaves, the roots arise, as in Aspidium Filix-mas, from the leaf- 

 stalks. In many Hymenophyllacese which have no true roots, branches of the stem 

 assume a root-like structure. In creeping and climbing species the leaves are sepa- 

 rated by distinct internodes which are sometimes very long ; in thick, ascending, 

 and vertical stems, the internodes are usually undeveloped, and the leaves so crowded 

 that no free portion of the stem remains uncovered, or only a very inconsiderable 

 one. The leaves of Ferns are usually characterised by a circinate vernation, and 

 they only unrol in the last stage of their growth ; the mid-rib and the lateral veins 

 are curved from behind forwards. The forms of the leaves are among the most 

 perfect in the whole vegetable kingdom ; they manifest an enormous variety in 

 their size, the lamina being usually deeply lobed, branched, or pinnate. In com- 

 parison with the stem and the slender roots they are mostly very large, and some- 

 times attain extraordinary dimensions, even a length of from lo to 20 feet (as in 



