62 SYDNEY H. VINES. 



scribed as occurring in Gyninosperms, in that it is developed, not 

 from a cell belonging to the suspensor, but from the tissue of 

 the embryo itself. It appears that in Selaginella we have the first 

 indication of that mode of the development of the root which 

 is more evident in Gymnosperms. 



The embryology of Isoctes, the other genus included in the 

 group Ligulatsc, although it has been investigated by Metteniu^/ 

 by lIofmeister,2 and quite recently by Bruchmann,^ is by no 

 means so clearly made out as that of Selaginella. Enough is known, 

 however, to show that there is a wide difference between the 

 modes of development of the embryo in the two plants. Accord- 

 ing to Bruchmann the oosphere of Isoeles is divided into two, 

 as is that of Selaginella, by a horizontal wall. The uj)per cell 

 grows rapidly towards the neck of the archegonium, and forms 

 the cotyledonary portion of the embryo. The lower cell grows 

 slowly downwards into the spore, and forms the hypocotyledonary 

 portion of the embryo. At the lower part of the anterior surface 

 of the cotyledon, a cell grows out into a prominence, from which 

 the " ligula" is subsequently formed. The cells lying immediately 

 at the base of this organ, give origin to the growing point of the 

 stem. From that part of the hy])ocotyledonary porf^ion of the 

 embryo which is diametrically opposite to the growing point of the 

 stem, the first root is developed, and the remainder of the hypo- 

 cotyledonary portion goes to form a mass of tissue to which the 

 name "foot" is given. From this brief account it appears that 

 the development of the embryo of Isoctes dirt'ers from that of 

 Selaginella in two principal particulars, viz. (1) that one of the 

 two primary cells gives rise, in the former, to a root and to a 

 foot, whereas in the latter a suspensor is developed from the cor- 

 responding cell ; and (2) that Isoetes possesses only one primary 

 leaf (cotyledon), whereas Selaginella possesses two. A discus- 

 sion of these points of difi'erence will follow in the concluding 

 paragraphs of this paper. 



The next group of plants to be considered is that of the 

 Rhizocarpepe, and of the plants included in it Marsilia and 

 Salvinia are those whose embryology has been most fully in- 

 vestigated. From the observations of Hansteiu* upon Mar- 

 silia, it appears that the oosphere is first divided by a nearly 

 vertical wall into two cells, one anterior,'' the larger, the other 

 posterior, and then each of these cells is divided by a septum at 



' Loc. cit. 



" 'Beit. z. Kciint. d. Gofiisskryptogamcn,' i, 1852. 



^ 'Jciiaisclic Zcitscliril't,' ISJI. 



* " Bcl'r. u. Eutwick. d. Gal.tung Marsilia," Priiigslieim's Jahrb., iv, 

 18G5. 



* The word anterior implies that this cell is the nearer to the apex of the 

 prothallus. 



