VASCULAR CRYPTOGAMS. 



IQT 



the embryo indicate llie rudiments of the first root, the first leaf and the apex 

 of the stem, while a lateral outgrowth of the tissue of the embryo, the so-called 

 foot, is formed at the same time at the bottom of the venter of the archegonium, and 

 draws the first nutriment for the embryo from the prothallium. The venter of the 

 archegonium grows vigorously at first in all except perhaps in the Selaginelleae, and 

 still incloses the embryo, but the latter at length emerges from it, leaving the foot for 

 a time still in it to serve as an organ of suction. In this we have an indubitable 

 analogy with the formation of the calyptra in the Muscineae. But while the sporo- 

 phyte in the Muscineae is never more than a mere appendage of the oophyte and 

 looks to a certain extent like its fruit, the corresponding generation in the Vascular 

 Cryptogams developes into a tall, highly organised, independent plant, whicii 

 becomes detached from the prothallium and supports itself at an early age. It is 

 this sporophyte which is usually termed absolutely a Fern or an Equisetum, &c., 

 and consists in all cases of a leafy stem, which usually produces a number of true 

 roots, though these may occasionally be wanting, as in many of the Hymenophylleae, 

 in Psilotum and in Salvinia. In many instances, especially in the true Ferns, Equise- 

 taceae and the fossil Lycopodiaceae, the sporophyte reaches a large size and the term 

 of its duration is unlimited ; only a few species are annual, as Salvinia, or very small 

 and with the habit of a Moss, as Azolla and some Selaginelleae. 



The leaves are either simple or repeatedly branched as in the Filicineae, but 

 there is not the variety in the forms of the leaves on the same plant, the result of 

 metamorphosis, which is found in the Phanerogams. 



The roots usually arise in acropetal succession on the stem, or in many Ferns 

 on the petioles, and their branching is either monopodial or dichotomous ; they are 

 uniform in character, and the first root never assumes the significance of a tap-root, 

 as happens in many Phanerogams ; nor do the lateral roots spring from the peri- 

 cambium of the primary root, as in Phanerogams, but from the innermost layer of 

 the cortex. 



The differentiation of the systems of tissue appears for the first time in great per- 

 fection in this group of plants ; dermal, fundamental and fascicular tissues are always 

 clearly discriminated and their elements assume a great variety of forms. The vascular 

 bundles are closed ; their phloem, the sieve-tube portion, usually surrounds the xylem, 

 the wood-portion of each bundle, as a sheath. 



The branching of the stem is different in the different divisions ; it may be mono- 

 podial, or decidedly dichotomous, or with a tendency to dichotomy ; axillary branching 

 such as that of the Phanerogams probably does not occur. 



The sporangia usually arise on ordinary or on peculiarly metamorphosed leaves ; 

 Schleiden's term sporophyll may be adopted for a fertile leaf, a leaf which bears 

 sporangia. In Selaginella the sporangia are produced from the growing-point of the 

 stem above the axil of a leaf; in Psilotum they are sunk in the extremity of branch- 

 lets of a peculiar form. A sporangium either originates in a single superficial cell, 

 as in the Ferns in the narrower use of the term including the Salviniaceae and 

 the Marsiliaceae, or a group of cells takes part in the formation of the sporangium, 

 as in all the other divisions. In both cases the tissue which produces the spores 

 proceeds, in the Vascular Cryptogams as in the INTuscineae, from an archesporiutn, 

 which is either a single cell, or a cell-row, or a ccll-Inyer. and makes its appearance 



