128 EMBRYOGENESIS IN PLANTS 



of approximately the same size. The next development consists in the 

 rapid growth of the root which bursts out from the tissue of the 

 prothallus, Fig. 31c; its vascular strand can be traced from the apex 

 backwards to the region of the root's inception close to the foot. The 

 foot meanwhile has not undergone any conspicuous enlargement and 

 the epibasal segment is still quite undift'erentiated histologically. 

 Development to this stage is said to occupy several seasons. The 

 embryo is filled with nutritive substances but contains no endophytic 

 fungus. In the next phase of development the shoot apex, the first leaf 

 (which is situated on the side of the axis above the first root), and a 

 surrounding leaf sheath, have their inception in a superficial, approxi- 

 mately median position in the epibasal segment. A column of elongated 

 cells, actually incipient vascular tissue, is now differentiated in the 

 tissue between the first leaf and the root stele, and the apex of the second 

 root is now organised. Text-fig. 3 Id. This first leaf undergoes some 

 further growth. The second leaf is formed at the apex in a normal 

 manner, its vascular strand becoming joined with the root stele. No 

 vascular tissue is differentiated below the apical meristem of the shoot. 

 The first and second leaves have sheathing bases like the leaves in the 

 adult shoot. The first leaf may be only slightly larger than the second, 

 and the latter is not enclosed in the leaf-base of the former. Fig. 31e. 

 In fact, the first leaf soon stops growing, but the second leaf grows on 



Fig. 31. Embryogeny in Ophioglossaceae 



A-E, Ophioglossum viilgatiim. A, Archegonium in l.s. showing the first division of 

 the zygote. B, An embryo in the post-octant phase, showing a regularly segmented 

 but undifferentiated ovoid tissue mass, consisting of the epibasal (ep) and hypo- 

 basal (hy) regions; the latter gives rise to the first root (/■) of which an endogenous 

 initial can perhaps be recognised, and the foot,/; I-I, first or basal wall. C, An older 

 embryo in l.s. showing the well-developed first root {r), the undifferentiated epibasal 

 region {ep), which will later give rise to the shoot apex and first leaf, and the foot (/) 

 in contact with the prothallus ip). D, Embryo in l.s. showing the shoot apex (s), the 

 first leaf (/), and its encasing sheath {Is), the first root (/) with its vascular strand 

 (vs), and the initial of the second root {r.^)- E, An older embryo in l.s., showing the 

 points indicated above, but here it can be seen that the first leaf (/i) has remained 

 small, while the second leaf (/o) is becoming conspicuous; each is enclosed in a leaf 

 sheath (after Bruchmann). F, Botryc/iiiim hiiiaria. First division of zygote, as seen in 

 l.s. of archegonium. The embryogeny, as in O. iiilgatum, is exoscopic (after 

 Bruchmann). G, H, B. obliquiiin. Archegonium with zygote as seen in l.s.; the 

 zygote elongates and penetrates the tissue of the prothallus. At the first division a 

 transverse wall divides this cell into a suspensor and an embryonic cell and the em- 

 bryogeny is endoscopic; a, archegonium (after Lyon). J-O, Helminthostacliys zey- 

 laiiica. J, Young arrested endoscopic embryo, consisting of first and second sus- 

 pensor tier cells (s^ and s.,), and the embryonic cell (e); ar, archegonial neck. K, 

 Mature embryo, seen from suspensor side, showing the suspensor (s.,), the foot (/), 

 the shoot apex (a), the root (r), and the first leaf (/). L, Basal region of young plant 

 showing the apical bud (a), the first leaf (/), the first and second roots (/"i, /-.>), the 

 hypocotyl (/;), and the foot (/); s, suspensor. M, N, Two small embryos, showing 

 the suspensor, the swollen embryo proper and the position of its apex {a). O, Pro- 

 thallus and embryo in approximately longitudinal section, showing the several 

 embryonic regions; lettering as above (after Lang). (A, x 150; B, x 225; C-E, 

 X 23; F, X 100; J, x 130; K-N, x 20.) 



