ON THE HOMOLOGIES OF THE SUSPENSOR. 61 



root. In the latter case, as has been already pointed out, the 

 root is derived from the hypophysis, i.e. from a cell belonging to 

 the suspensor. In the former case it appears, from the researches 

 of Strasburger, that the root is entirely developed from the tissues 

 of the embryo itself. 



In passing from the Gymnosperms to the higher Cryptogams 

 we come first to the class of the Dichotomese. Of the embryology 

 of the members of one subdivision of this class, that of the 

 Lycopodiacese, comparatively little is known, whereas that of the 

 members of the other subdivision, the Ligulatse, has been to some 

 extent investigated. Pfeti'er^ has given a very full account of 

 the development of the embryo of Selaginella, one of the two 

 genera included in the group Ligulatge. According to him the 

 first division of the fertilised oosphere of the archegonium takes 

 place in a horizontal plane, and thereby two cells are formed, an 

 upper and a lower. The upper cell, usually after having under- 

 gone divisions, becomes elongated and forms the suspensor. The 

 lower cell is divided by a septum, 2 (fig. 3), which is nearly at right 

 angles to the plane of the first septum, into two equal segments, 

 (a and b), and of these two segments one (a) is further subdivided 

 by the formation of a wall, 3, which extends from about the 

 middle of the height of wall, 2, to the external wall of the cell. 

 By this means a wedge-shaped segment (c) is formed, which is the 

 apical cell of the embryonic axis. In the remaining portion of 

 segment a a wedge-shaped cell is formed, which is immediately 

 adjacent to the segment c, and a similar cell is formed in a corre- 

 sponding position in segment b. These two cells are the apical 

 cells of the two first leaves (cotyledons) fig. 3, a. The remainder 

 of segment a contributes to the formation of the hypocotyle- 

 donary axis, as does also that portion of segment b which lies 

 immediately behind the apical cell of the leaf which arises from 

 it (fig. 3, b). From the cells still further back, the structure 

 to which Pfeti'er gives the name of "foot," is developed, and 

 lying back between the foot and the suspensor are some cells 

 from which the root takes its origin. 



On comparing the development of the embryo of Selaginella 

 with that of the embryo of an Angiosperm, it is at once apparent 

 that the suspensor in each case is developed in the same manner, 

 and the one is therefore the homologue of the other. There 

 appears to be a development, in Selaginella, of a new organ, the 

 foot, which has no representative in the embryo either of aGym- 

 nosperm or of an Angiosperm. The pr'tpriety of applying the term 

 "foot^' to this structure will be discussed hereafter. Further, the 

 mode of development of the root of Selaginella differs from that 

 obtaining among Angiosperms, and resembles that above de- 



' Loc. cit. 



