XV] 



EMBRYOS OF OPHIOGLOSSACEAE 



305 



from the archegonial neck, and later a change in direction of growth results 

 in the shoot pointing vertically upwards, and the root downwards (Fig. 289). 

 The development of the embryo is now well known in Botrychiuin 

 {Sceptridiinn) obliquiiiu (Campbell, Ajui. of Bot. xxxv (1921), p. 141, where 

 references are given). The arche- 

 gonial neck is directed upwards. 

 The zygote while still undivided 

 grows into an elongated tube, 

 which penetrates by an irregular 

 course into the tissues of the 

 prothallus (Fig, 290). Its nucleus 

 settles down to the distal end as 

 the growth proceeds. A transverse 

 wall apparently in a horizontal 

 plane separates the embryo proper 

 from the suspensor ; it is followed 

 by a second division, by a "basal" 

 wall, in the terminal cell or embryo, 

 which then consists of epibasal and 

 hypobasal tiers. The embryo thus 

 constituted develops further along 

 lines corresponding to those of 

 the Marattiaceae. The epibasal 

 hemisphere gives rise to the stem- 

 apex and the cotyledon, the latter 

 being the more marked feature. 

 The hypobasal hemisphere forms 

 the foot, and the first root origi- 

 nates " near the centre of the 

 embryo, very near the basal wall " 



Fig. 289. Botrychiuin [Sceptriditiiii) obliqutun, Muhl. 

 Photo-micrograph of a section through a ganieto- 

 phyte and young sporophyte. The root has already 

 protruded from the under side of the gametophyte. 

 a = archegonium ; j = suspensor ; t = stem-tip ; /= first 

 leaf; ;■= root. ( x 60.) (After H. L. Lyon.) 



(Campbell). As in Helminthostachys the original direction of growth alters 

 by strong curvature of the embryo. This has the effect of turning the apex 

 of the stem and leaf upwards, while the root projects vertically downwards, 

 penetrating the tissue of the foot (Fig. 289). In both cases a strong curvature 

 away from the original line of growth of the embryo was necessary to produce 

 this result ; and the degree of that curvature is brought into prominence in the 

 case o{ Botrychiuin by examination of the section taken in a horizontal plane 

 through the developed embryo of the age shown in Fig. 289. Here, though 

 the suspensor is traversed, the apex of the embryo is still seen in surface 

 view (Fig. 291). No suspensor has been found in any other species oi Botry- 

 chiitin or of Ophioglossimi so far examined. The orientation of their embryos 

 within the archegonium is, however, inverted as compared with those of 



