ON THE HOMOLOGIES OF THE SUSPENSOR. 67 



and Liverworts. The mass of cells in the embryo of Selaginella, 

 to which Pfeffer gives the name " foot," is certainly not homo- 

 logous with the foot of the other Cryptogams, nor is it analo- 

 gous to it. The function of the foot appears to be to serve for 

 a time as a means of connection, though not of organic connec- 

 tion, between the embryo (sporophore) and the prothallus 

 (oophore). It is quite evident that this function is discharged 

 in Selaginella, not by the so-called foot, but by the suspensor. 

 The word foot can, therefore, be no longer rightly applied to the 

 dilated hypocotyledonary portion of the stem of Selaginella. 



The products of the division of the embryophore of ferns, of 

 Marsilia, and of Isoetes, are differentiated at an early stage, one 

 portion giving rise to the foot, the other to the root, and a similar 

 differentiation also takes place in the case of Angiosperms, but at 

 a later stage. '^h.Q complete homology of the suspensor of Angio- 

 sperms with the foot of JbVrns, of Marsilia, and of Isoetes, is thus 

 made apparent. The analogy between these organs is also clear. 

 In these Cryptogams the foot serves as a connection between the 

 embryo and the prothallus. In Angiosperms the only represen- 

 tatives of the prothallus are the antipodal cells. In conse- 

 quence of this rudimentary nature of the prothallus the em- 

 bryophore becomes attached, not to it, but to the wall of the 

 embryo-sac (macrospore), and developes into the suspensor. 



It has now been shown that the seta and foot of Mosses and 

 Liverworts, the foot of the vascular Cryptogams,^ the suspensor of 

 Selaginella, of Gymnosperins, and of Angiosperms, are derived from 

 that cell, produced by the division of the oospore, to which, for the 

 sake of clearness, the name of embryophore has been given. 

 These organs may, therefore, be regarded as being truly homo- 

 logous, and this view is not invalidated with by the fact that the 

 suspensor or the foot is developed, in some cases, from the whole 

 of the embryophore, in others from a part only of it. This fact 

 merely renders the homology incomplete in certain cases. 



^ In consequence of the existing uncertainty with regard to the mode of 

 development of the embryo of Equisitace£E, this generalisation must not be 

 regarded as applying to tliat group. 



