356 PART IV. CLASSIFICATION. 



SPOROPHYTE. The stem is small, unbranched, short and tuberous, with 

 either two or three longitudinal furrows which give it a lobed appearance. 

 It is closely covered with numerous, relatively long (1-12 in.), sessile 

 leaves. From the furrows of the stem there spring numerous, dicho- 

 itemously branched, somewhat fleshy roots. 



The growth in length of the stem, which is very slow, is effected by an 

 apical growing-point consisting of several initial cells. The growing- 

 point of the root consists of small-celled meristem, and presents a similar 

 differentiation to that of the root of Dicotyledons (see p. 102). 



The leaves are either fertile or sterile ; the fertile leaves each bear a 

 single sporangium, and are termed macrosporophylls or microsporophylls 

 in accordance with the nature of the sporangium which they severally 

 bear. The order of development of the leaves in each year is that first of 

 all macrosporophylls are produced, then microsporophylls, and finally a 

 few sterile leaves in some species. Hence, when the development is com- 

 pleted, the macrosporophylls are external in the rosette, the sterile leaves 

 (when present) internal, and the microsporophylls intermediate. The 

 sterile leaves persist during the winter, and form a protection in the next 

 spring to the young leaves developed internally to them at the growing- 

 point. 



The fertile leaves, whether macro- or micro-sporophylls, consist of a 

 broad, sheathing base, with membranous margins, which bears a narrow 

 subulate lamina, flattened somewhat on the upper (ventral) surface. 

 Close above the insertion, on the upper or inner surface of the leaf-base, is 

 a pit, the fovea, in which the single sporangium is situated. In some 

 species the margin of the fovea is prolonged into a membrane, the velum. 

 which either partially (e.g. 1. lacustris}, or completely (terrestrial species), 

 covers the sporangium. Above the fovea, in the middle line, is another 

 smaller pit, the foveola, occupied by the somewhat swollen base of a pro- 

 jecting flattened membranous structure, the ligule, which is developed 

 from a single superficial cell of the young foveola, and is relatively much 

 larger in the quite young leaf than in the adult. 



The sterile leaves are less highly developed than the fertile ; they are 

 smaller, especially as regards the leaf -base. In the terrestrial species they 

 are reduced to scaly cataphyllary leaves of a brown colour. 



The sporangium is developed from a group of cells in the fovea. The 

 archesporium consists of a layer of hypodermal cells in the young 

 sporangium. In a microsporangium all the archesporial cells grow and 

 divide so as to form rows radiating from the free surface to the attach- 

 ment of the sporangium. Some of these rows of cells soon cease to grow, 

 and are not sporogenous, but remain as plates of tissue, termed trnbecufa; 

 which imperfectly chamber the cavity of the microsporangium. Of the 

 remaining cells, the majority constitute the mother-cells of the micro- 

 spores invested, towards the wall of the sporangium, by sterile cells 

 forming the tapetum. In a macrosporangium, the fertile archesporial 

 cells undergo but a single division, whilst the trabeculae are formed as in 

 the microsporangium. The large mother-cells of the macrospores are 

 isolated, and each is invested by a tapetal layer. Each spore-mother-cell 

 gives rise, finally, to four spores. 



