EMBRYOGENESIS IN THE LYCOPODINEAE 121 



Study. When the zygote divides, the first partition wall is laid down in a 

 vertical-oblique position relative to the archegonial axis (it is off-set at 

 an angle of about 20^), and where the archegonium is horizontal, it is 

 at right angles to the direction of gravity. Fig. 29h. Only rarely was 

 this wall observed in a position at right-angles to the archegonial axis. 

 Moreover, the tilt of this wall is such that a peripheral point nearest the 

 archegonial neck is in the highest position (relative to the zenith) of the 

 apex of the venter, Fig. 29h-k. 



The innermost of the two cells is described by La Motte as the 

 epibasal segment. A second wall divides both segments, somewhat 

 unequally, the two quadrants next the archegonial neck being somewhat 

 smaller than the other two. Of the latter, i.e. in the base of the venter, 

 the cell nearest the zenith is the larger. An octant stage follows. The 

 cell divisions now cease to be simultaneous, more rapid growth and 

 division being characteristic of the cells in the base of the venter. Fig. 

 29l, m. La Motte's illustrations. Fig. 29n-q, show the further develop- 

 ment of the embryo, its several members being related to the early 

 segmentation described above. It will also be seen that he considers 

 the embryogeny to be endoscopic and not exoscopic as previous 

 investigators had supposed. The innermost epibasal quadrant gives 

 rise to the first leaf and the outermost one to the slowly-organised shoot 

 apex; the innermost hypobasal quadrant becomes the foot and that 

 next the archegonial neck the first root. This embryonic development 

 is thus like that of a leptosporangiate fern, which the present writer 

 would prefer to describe as being lateral. La Motte considers that, on 

 various grounds, the Isoetales should be regarded as being coordinate 

 with the Lycopodiales and therefore included in the division Lycopsida. 



APOGAMY 



The apogamous development of embryos in Selaginella has been 

 reported in 5'. rubricaiiUs and S. spimdosa by Bruchmann (1912), and 

 in S. anocardia by Goebel (1915). The details of development, in so 

 far as they are knov/n, appear to follow the normal pattern. If this is so, 

 the biochemical differentiation which leads to the formation of an 

 axial embryo must be present in the unfertilised ovum. 



FOSSIL EVIDENCE 



Although some rather good specimens of fossil megaspores with 

 prothalli have been obtained, e.g. Borthrodendron from the Lower 

 Coal Measures, nothing is known of the embryology of the arborescent 

 fossil Lycopodineae. 



