SECT. I CRYPTOGAMS 445 



the basal wall. By the further division of these eight cells a small 

 mass of tissue is formed, and from this are developed the stem apex, 

 the first leaf, the primary root, and an organ peculiar to the Pterido- 

 phytes, the so-called foot (Fig. 389, /). 'xhe foot is a mass of tissue, 

 by means of which the young embryo remains attached to the parent 

 prothallium and absorbs nourishment from it, until, by the develop- 

 ment of its own roots and leaves, it is able to nourish itself inde- 

 pendently. The prothallium then usually dies. The stem developed 

 from the embryonic rudiment may be either simple or bifurcated, erect 

 or prostrate ; it branches without reference to the leaves, which are 

 arranged spirally or in whorls, or occupy a dorsiventral position. 

 Instead of rhizoids, as in the Bryophyta, true roots are produced, as in 

 the Phanerogams (cf. Fig. 1 1 6). The leaves also correspond in structure 

 with those of the Phanerogams. Stems, leaves, and root are traversed 

 by well-differentiated vascular bundles, and the Pteridophytes are, in 

 consequence, designated Vascular Cryptogams. The bundles of the 

 great majority of Pteridophytes are as a rule constructed on the 

 concentric type (cf. Fig. 390 and Fig. 135). Secondary growth in 

 thickness, resulting from the activity of a special cambium, occurs 

 only occasionally in existing forms, but it was characteristic of the 

 stems of certain extinct groups of Pteridophytes. 



The SPORES are produced vegetatively in special receptacles termed 

 SPORANGIA, which occur on the asexual generation, either on the 

 leaves, or less frequently on the stems in the axils of the leaves. 

 The leaves which bear the sporangia are termed SPOROPHYLLS. The 

 sporangium consists of a wall enclosing the sporogenous tissue, the 

 cells of which, becoming rounded off and separated from each other 

 as spore-mother-cells, give rise each by a reduction-division to four 

 tetrahedral spores (spore-tetrads). The cells of the innermost layer of 

 the sporan^ial wall are rich in protoplasm, and constitute the TAPETUnr. 

 This layer persists in the Lycopodineae, but in the case of the Ferns 

 and P]qui.setineae the walls of the tapetal layer become dissolved. In 

 the course of the development of the sporangium the tapetal cells 

 then wander in between the spore-mother-cells, so that the spores 

 eventually lie embedded in a mucilaginous protoplasmic mass, the 

 PERIPLASM, from Avhich they derive nourishment. The wall of the 

 mature sporangium is formed of one or a number of layers of cells. 

 The unicellular spores have cell-walls composed of several layers. 



The spores of the majority of the Pteridophytes are of one 

 kind, and give rise on germination to a prothallium, which produces 

 both antheridia and archegonia. In certain cases, however, the 

 prothallia are dioecious. This separation of the sexes extends in 

 some groups even to the spores, which, as macrospores (megaspores), 

 developed in macrosporangia (megasporangia), give rise only to 

 female prothallia ; or as microspores, which are produced in 

 MICROSPORANGIA, develop similarly only male prothallia. In accord- 



