XIII 



EQUISETINE^Z 



433 



deeply sunken in the prothalHal tissue than is common in the 

 Ferns. The basal wall is transverse, as in the Marattiaceai, and 

 the formation of the quadrants takes place as usual. The 

 position of the quadrant walls is, however, sometimes slightly 

 different, being often decidedly inclined in both epibasal and 

 hypobasal halves (Fig. 225, F). In the former the larger of 

 the two primary cells is the initial for the stem, and its large 

 size, compared to the leaf quadrant, already points to the 

 greater development of the stem in the sporophyte compared 



Fig. 225. — A, Longitudinal section of the venter of a recentlj- fertilised archegonium, x 300 ; li, a 

 similar section of an archegonium with the young embryo ; C, D, two transverse sections of a 

 somewhat older embryo, X 300 ; st, apical cell of the stem ; r, apical cell of the root ; E, 

 longitudinal section of an older embryo, X300; I, I, the basal wall. 



to the leaves. Of the hypobasal quadrants the larger becomes 

 at once the root, whose axis is coincident with that of the stem. 

 The first two divisions in the stem quadrant establish the 

 definitive apical cell, which occupies nearly the centre of the 

 epibasal part of the embryo, and is surrounded by a circle of 

 four cells, two of which belong to the leaf quadrant (Fig. 225, 

 C), and two are segments of the stem quadrant, the first one 

 corresponding morphologically to the second leaf of the Fern 

 embryo. This circle of cells forms the first sheath about the 



2 F 



