420 PART III. THE CLASSIFICATION -OF PLANTS. 



hypobasal octants, one gives rise to the growing-point of the primary root, and 

 two to the foot. 



The primary stem grows erect, and its leaf-sheaths are three-toothed, the 

 three leaves corresponding to the three segments cut off from the apical cell of 

 the stem ; it branches at its base ; stouter shoots with an increasing number of 

 teeth in the leaf-sheaths are successively produced, and eventually a branch is 

 produced which becomes the perennial subterranean rhizome. 



The GAMETOPHYTE is a green, dorsiventral, lobed prothallium which becomes 

 quite free from the spore. The prothallia are generally dioecious, the female 

 prothallia being larger than the male ; but the distinction of sex is not absolute, 

 for the female prothallia may eventually bear male organs, and the male pro- 

 thallia female organs ; it appears to depend largely on conditions of nutrition. 



The germinating spore divides into two cells : one of these contains no 

 chloroplastids, and grows out into a hair which represents a root (see p. 61), 

 the other contains chloroplastids, and grows and divides to form the first lobe 

 of the prothallium, which branches as its development proceeds, some of the 

 branches of the female prothallia growing erect. On its under surface the 

 prothallium bears numerous root-hairs.. 



At first the prothallium consists throughout of a single layer of cells ; in the 

 female prothallium, however, one of the lobes becomes thick and fleshy, con- 

 sisting of several layers of cells formed by repeated horizontal cell-division, and 

 this constitutes the archegoniophore. 



The male organ, or antheridium, is developed from a single cell of the margin 

 of the male prothallium : this cell undergoes repeated division, with the result 

 that a wall, consisting of a single layer of cells, is formed surrounding a central 

 cell from which, by subsequent divisions, the numerous mother-cells of the 

 male cells are developed : the antheridium eventually dehisces by the separa- 

 tion of the cells forming the roof, in consequence of the swelling-up of the con- 

 tents of the antheridium. The male prothallium bears several antheridia, one 

 being developed terminally on each lobe, and others in succession on the lateral 

 margins. 



The male cell, or spermatozoid, is larger than that of any other Pteridophyta ; 

 it has only two or three coils, and bears a tuft of short cilia at its anterior 

 pointed end. 



The female organ, or archegonium, resembles, in all essential features of its 

 structure and development, that of the typical Filicinee : a distinctive peculi- 

 arity is afforded by the long recurved terminal cells of the neck, and by the 

 relatively small neck-canal-cell. Each prothallium bears a number of these 

 organs : they are developed each from an anterior marginal cell, and, as the 

 prothallium continues to grow, the organs come to lie on its upper surface. 



The female cell is an oosphere, and calls for no special remark. 



