1896-97-] THE GAMETOPHYTE OF BOTRYCHIUM VIRGINIANUM. 279 



the ensuing divisions, figure 44. Quite often, too, no regular course of 

 segmentation can be made out at all, as in figure 45. When the embryo 

 is only a little larger than those figured in 43, 44 and 45, the basal, 

 median, and transverse walls are quite obscured by subsequent divisions. 

 It is not possible to detect any indication of apical initials such as 

 commonly occur in the early phases of the leptosporangiate sporophyte, 

 and such as have also been described in some, at least, of the eusporan- 

 giate Pteridophyta. The next phase which is chosen for representation, 

 is that in figure 46. Although no apical cells could be made out in 

 this preparation and others of the same age, there is in the example 

 figured, a very considerable formation of periclinal walls in the upper 

 internal region of the embryo. The whole lower portion of the young 

 sporophyte forms the foot, figure 46 /i In figure 47, is shown an 

 embryo in which the root and shoot have already become differentiated. 

 The periclinal activity already referred to, has led to the formation of a 

 large amount of tissue in the upper portion of the embryo, and this is 

 supported on the broad basis furnished by the foot. A high merismatic 

 epidermis has already become differentiated at x, the cells of which are 

 very rich in protoplasm and have the elongated columnar configuration 

 of the shoot meristemeta of most of the Pteridophyta. Among these, 

 the one marked a seems to be the initial cell. At v, is a protuberance 

 which is the outward indication of the first root. Within this, at b, is 

 the apical cell of the root, distinguished by its darkly-stained proto- 

 plasm, and by the fact that it has just undergone its first periclinal 

 division. The condition of the embryo of Botrychimii virginiamim at 

 this stage, is remarkable in that the stem-apex appears before the first 

 leaf The cotyledon is consequently derived from the shoot meristem, 

 just as the later leaves are, but as in the case of the latter, it is not 

 possible to follow the changes in the meristem leading to the formation 

 of the foliar rudiment. The difficulty is greater in the case of the 

 cotyledon, on account of the comparative paucity of younger embryos 

 which have been cut exactly axially. For this investigation nearly 

 three hundred series o prothalli, from two to twenty millimetres in 

 length, have been sectioned. In spite of this not inconsiderable labor, 

 less than twenty per cent, proved to be of value, either because no 

 embryos were present, which is very commouly the case ; or being 

 present, they were not cut in a truly median plane. The surface of the 

 gametophyte presents such irregularities that the proper orientation of 

 the younger phases of the embryo is entirely a matter of chance. So far 

 as I am aware the embryo of the Equisetacece presents the only other 

 case yet described, in which the primitive foliar organ is secondarily 



