FILICINEA E. HOMOSPOR US FILICINEAE. 



205 



f I 



have been clearly ascertained by modern investigations, which correct Hofmeister's 

 earlier observations. The part of the embryo which is towards the underside 

 of the prothallium will in the following description be called the upper part 

 (marked | in Fig. i 3), t e part 

 towards the neck of the arche- 

 gonium the under part (+ in 

 Fig. 153); the anterior half is 

 the half which is turned towards 

 the growing point of the pro- 

 thallium. The arrangement of 

 the cell walls ' presents nothing 

 unusual; it agrees with that of 

 other organs with a similar out- 

 line, as is shown by the young 

 gemma of Marchantia, which is 

 given in Fig. 153 B for the pur- 

 pose of comparison. The first 

 wall is nearly coincident with the 

 axis of the archegonium ; it is 

 called the basal wall (Fig. 153 b b), 

 and divides an anterior half of 

 the embryo, the half which forms 

 the stem, from the posterior half 

 which forms the root; Leitgeb 

 calls the anterior half the eptbasal, 

 the posterior the hypobasal half. 

 Two fresh walls then make their 

 appearance at right angles to the 

 basal wall and to one another, and 

 divide the embryo into octants. 

 The order of appearance of these 

 walls is variable; one called the 

 transversal wall (Fig. 153 / /) runs 

 parallel to the surface of the pro- 

 thallium, the other, the median wall 

 (Fig. 153 m m), which is not 

 visible in A, being in the plane of 

 the paper, is at right angles to the 



surface of the prothallium. Of the two anterior upper octants one becomes the grow- 

 ing point of the stem, the other undergoes as a rule no further differentiation; the 

 two anterior lower octants develope into the first leaf, the cotyledon ; the two posterior 

 upper octants form the foot, and one of the two posterior and lower ones forms the 

 root, while the other does not usually develope like the rest. Two walls then appear 



1 A clear idea of the construction of the embryo may be obtained by marking the walls on an 

 ovoid or round wooden model separable into four or eight pieces, such as any turner can supply. 

 See Goebel, Zur Embryologie d. Archegoniaten (Arb. d. bot. Inst. Wiirzburg, Bd. II). 



f 



FIG. 153. A, C, D Diagrammatic representations of the cell-division in 

 the embryo of the Filicineae, from a model. B young gemmae of Marchantia 

 polymorpha; b basal, t transversal, m median wall, h hypobasal, e epibasal 

 wall, s rudiment of the apex of the stem, TV root, co cotyledon, f foot. The 

 numbers serve to distinguish the walls in the different figures (the 5 in D 

 should be s). The arrow indicates the direction of the apex of the prothallium, 

 the mark | the underside of the prothallium, + the neck of the archegonium. 

 A is a side view of an upright embryo in a prothallium. C is a view of A 

 rotated through an angle of 90 degrees, the axis of rotation being the line of 

 intersection of the transversal with the median wall. D anterior view of A 

 and C also rotated through an angle of 90 degrees, the axis of rotation being 

 the line of intersection of the transversal with the basal wall. E same view 

 as A, but lying down, not upright, and showing an em.ryo of Ceratopteris 

 after Leitgeb. 



