INTRODUCTION. 
its entry into the archegonium. The mother-cells of the antherozoids arise in the 
antheridia, which in Ferns and Equisetaceae project free from the prothallium as 
roundish masses of tissue, but in the Ophioglosseae and Lycopodium are imbedded 
in the prothallium. Among Rhizocarpese, Salvinia forms a very simple antheridium 
which projects from the microspore, while the Marsiliacese and Selaginelleog pro- 
duce their antherozoids within the microspore itself, after a few-celled mass of 
tissue has been formed in it which must be considered as a rudimentary 
prothallium. 
The Asexual Generation [Sporophore] which produces spores, arises from the 
oospore or fertihsed oosphere in the archegonium. In Ferns, Equisetaceae, and 
Rhizocarpeae, its earhest divisions, the rudiments of the first root, the first leaf, and 
the apex of the stem can be recognised, while at the same time a lateral outgrowth 
of its tissue, called the Foot^ commences at the bottom of the ventral part of the 
archegonium, and draws from the prothallium the first nourishment for the young 
plant. The ventral part of the archegonium at first grows vigorously (except appa- 
rently in the Selaginelleas), enveloping the embryo, until this latter finally protrudes 
free, leaving however, for some time, the foot still attached to it as a nutritive organ. 
This process off"ers an unquestionable analogy to the formation of the calyplra of 
the Muscineae. While, however, the spore-producing generation of the Muscineae 
remains a mere appendage of the sexual plant, appearing in a certain sense as its 
fruit, the corresponding generation of Vascular Cryptogams developes, on the con- 
trary, into a conspicuous, highly organised, independent plant, which frees itself at a 
very early period from the prothallium, and obtains its own nourishment. It is this 
asexual generation which is called, in ordinary language, simply the Fern, Equisetum^ 
&c. ; it always consists of a leafy stem, usually producing a number of true roots ; 
roots may, however, occasionally be entirely absent, as in some Hymenophyllaceae, 
and in Psilotum and Salvhiia. In many cases, especially in Ferns, Equisetaceae, and 
(especially the extinct) Lycopodiaceae, the spore-producing generation attains great 
dimensions with an unlimited term of life ; only a few species are (like Salvinia) 
annual, or very small, resembling Mosses in habit, as Azolla and some Selaginelleae. 
The Leaves are either simple, unsegmented, or variously branched (Fihcineae). 
There does not, however, occur so great a variety due to metamorphosis in the 
forms assumed by the leaves in the same plant as in Phanerogams. 
The Roots usually arise in acropetal succession on the stem (or on -the leaf- 
stalk in some Ferns), and branch monopodially or dichotomously ; they always 
remain nearly uniform in size, the first root never attaining the dimensions of a 
tap-root, as in many Phanerogams. The lateral roots do not arise, as in Phanero- 
gams, from the pericambium, but from the innermost cortical layer of the main 
root. 
The Differentiation of the Systems of Tissue attains a high degree of perfection 
for the first time in this group of plants. The epidermis, fundamental tissue, and 
fibro-vascular bundles are always clearly distinct, and are composed of cells of 
various forms. The fibro-vascular bundles are closed ; the phloem usually sur- 
rounds the xylem of each separate bundle like a sheath. 
The Branching of the Stem is very diff"erent in the diff'erent classes of Vascular 
Cryptogams ; it is essentially monopodial, but it is often apparently dichotomous : 
c c 2 
