INTRODUCTION. 387 



its entry into the archegonium. The mother-cells of the antherozoids arise in the 

 antheridia, which in Ferns and Equisetacese project free from the prothallium as 

 roundish masses of tissue, but in the Ophioglossese and Lycopodium are imbedded 

 in the prothallium. Among Rhizocarpeae, Salvinia forms a very simple antheridium 

 which projects from the microspore, while the Marsiliaceae and Selaginelle^B 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 fertilised oosphere in the archegonium. In Ferns, Equisetaceae, and 

 Rhizocarpeae, its earliest 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 offers an unquestionable analogy to the formation of the calyptra 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, Equisetuniy 

 &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 Salvinia. 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 (FiUcineae). 

 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 different in the different classes of Vascular 

 Cryptogams ; it is essentially monopodial, but it is often apparently dichotomous : 



c c 2 



