8o 



OPHIOGLOSSACEAE 



[CH. 



Fig- .^80. Development of the archegonium in Ophioglossiim pendulum (after Camp- 

 bell) ( X 135). A, transverse section of the gametophyte apex, showing two young 

 archegonia ? , and apical cell (x). B-G, successive stages in the development of 

 the archegonium, seen in longitudinal section: «, neck canal cell; b, basal cell. 

 H, recently fertilised archegonium: sp, a spermatozoid within the egg-nucleus. 



Embryology. 



The embryology of the Ophioglossaceae has gained greatly in interest 

 and in morphological importance from recent observations. Its variable 

 features will be seen to run parallel with the results of the foregoing com- 

 parisons of the sexual organs. In the '' ternatiini' group of the genus Botry- 

 chmm,diS, seen in B. obliquiun, the embryo is furnished with a suspensor, and 

 the embryogeny is endoscopic (see Vol. I, Chapter XV). The zygote elongates, 

 penetrating deeply into the prothallus at first without division (Fig. 381). 

 The embryo itself is formed at the tip of this suspensor, and its parts are 

 differentiated relatively early. These are essentially similar to those of 

 other species of the genus: the first leaf (cotyledon) appears on the side of 

 the axis directed obliquely upwards, and it breaks through the upper surface 

 of the prothallus: the root originates on the side directed downwards, and 

 it emerges on its under side (Fig. 382). Campbell has shown that a basal 

 wall separates, as in other Pteridophytes, an epi basal from a hypobasal 

 hemisphere. The former gives rise to the stem-apex and the cotyledon, 

 while the root originates centrally very near to the basal wall, so that it is 

 difficult to say whether it belongs to the epibasal or the hypobasal region 

 {Ann. of Bot. 192 1, p. 141). In the course of this development, since the axis 

 of the archegonium is oblique the embryo has to execute a more or less 

 sharp curvature so as to secure that its apex shall point upwards, and the 

 root emerge downwards, as it is seen to do in Fig. 382. It will be realised 

 that this is a consequence of the presence of the suspensor and of the endo- 

 scopic orientation. 



The embryogeny of Eu-Botiychium (B. Lunaria and simplex) differs frorn 

 this in the fact that there is no suspensor, and the embryo shows no curva- 

 ture, being exoscopic in orientation, and the archegonium pointing usually 

 upwards. The octant-walls appear directly in the zygote itself, and they are 



