BOTANY 



which becomes the asexual generation, as in the Bryophyta. The 

 Bryophyta and Pteridophyta have accordingly been classed together as 

 Embryopkyta by Englee, and termed Embryophyta zoidiogama, because 

 the male cells are developed as spermatozoids. 



The asexual generation or sporophyte is represented by a plant 

 possessing a highly differentiated internal structure, and externally 

 segmented into stem, leaves, and roots. In the majority of Pterido- 

 phytes, the fertilised egg-cell, while still in the archegonium (Fig. 

 339), surrounds itself with a cell wall and undergoes division, first 

 into two cells, by the formation of a transverse or basal wall, and then 

 into octants by two walls at right angles to each other and to the 

 basal wall. By the further division of these eight cells the half above 

 the basal wall gives rise to the tissues of the stem apex and the first 



leaf, while from the 

 half below the basal 

 wall is produced the 

 primary root, and an 

 organ peculiar to the 

 Pteridophytes, the so- 

 called Foot (Fig. 331, 

 A, B). The foot is 

 a mass of tissue, by 

 means of which the 

 young embryo remains 

 attached to the parent 

 prothallium and ab- 



Fia. 331.—^, Pteris serrulata, embryo freed from the archegonium, sorbs nourishment 



in longitudinal section (after Kiemtz-Gekloff) : I, basal wall; f -a 11T ,f;i y, v +V, P 



II, transverse wall dividing the egg-cell into quadrants, rudi- Irom "j Until, uy Lilt; 



ment of the foot /, of the stem s, of the first leaf 6, of the root development of its Own 



w ; B, section of a further-developed embryo of Pteris aquilirut j-oots and leaves it is 



(after Hofmeister); /, foot still embedded in the enlarged . ">,'•+ If 



ventes of the archegonium aw ; pr, prothallium. (Magnified.) a tH6 to nOUriStt ltselt 



independently. 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, true roots are produced, as in the Phanerogams. 

 The leaves also correspond in structure with those of the Phanero- 

 gams. Stems, leaves, and root are traversed by well -differentiated 

 vascular bundles, and the Pteridophytes are, in consequence, designated 

 Vascular Cryptogams. The bundles, which as a rule have the same 

 structure throughout the whole group, are constructed after a special 

 type (cf. pp. 104, 114, and Figs. 121, 127, 128). 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. 



