672 CONCLUSION 



origin of the first root is again fully illustrated within the Lycopods : 

 in Se/aginel/a (Fig. 190) the first root originates laterally from the hypo- 

 basal tier, and near to the suspensor : in Lycopodium (Figs. 183, 185, 

 186, 188) and in Jsoetes (Fig. 191) it springs from the epibasal tier, and 

 is thus necessarily in a lateral position upon the whole embryo. Its 

 orientation relatively to the cotyledon also varies : in Isoetes it is opposite 

 to the cotyledon (Fig. 191), in Lycopodium and Selaginella it is frequently 

 on the same side of the axis as the cotyledon, but this is not constant 

 in S. spinu/osa : in Ferns it is on the same side as the cotyledon (Fig. 

 15). It thus appears that the root is not definite in level or in orienta- 

 tion relatively to the other parts ; while in point of time, its extreme 

 delay in L. cernuum and its absence in Sah'inia are cases too well 

 known to require remark. It is notable that though the root in Seed- 

 Plants directly faces the suspensor, this is not the case in any Pteri- 

 dophyte : in them it is always a lateral appendage, however nearly it may 

 sometimes approach the centre of the hypobasal hemisphere. Accordingly 

 it cannot be held to be itself the continuation of the primitive axis. 



Though the root may appear late in the embryology of certain Lycopods, 

 the converse is seen in the Ophioglossales ; in them the precocity of the root 

 upsets the balance of parts usual in other embryos. This is seen in moderate 

 degree in such types as Botrychium virginianum (Fig. 261) or B. obliquum 

 (Fig. 264), in which, though the embryo differentiates slowly, the root soon 

 takes a prominent place; but in Botrychium Lnnaria (Fig. 263) and 

 Ophioglossum milgafinn (Fig. 260, 260 Ins) it is clear that the root, rushing 

 forward in its development, outstrips the other parts, and becomes the 

 prominent feature of the embryo. The extreme is, however, found in 

 Oph. pendulum, and so prominent is the root here that Campbell has 

 described the embryo as consisting of "roots only." 1 This may probably 

 be held as the consequence of precocity of the root carried to a greater 

 degree than in other species : and the precocity finds a ready biological 

 meaning in its mycorhizic function. It may be held that the embryo 

 hurries it forward as an accessory aid to nutrition, and the parts of the 

 shoot are correlatively delayed till sufficient store is at hand to justify 

 their development above ground. 



Though the balance of parts in the embryo may be thus disturbed by 

 the precocity of certain parts, still more profound disturbances appear 

 associated with parenchymatous swellings of the nature of haustoria or of 

 storage tubers, and these are usually accompanied by considerable curvature, 

 and distortion of the axis. Such swellings are of two sorts : intra-prothallial 

 haustoria, to which the name " foot " has commonly been applied, and 

 extra-prothallial tubers, known under the name of " protocorm." In simple 

 types of embryo with suspensor the hypobasal tier of the embryo may 

 remain small, though functionating as an haustorium (L. Xe/axo, Fig. 183, 

 and L. Phhgmciria, Fig. 185): but in others it may enlarge in the direction 



1 Ann. /an/. /?//., vol. xxi., p. 189. See remarks on p. 469 above. 



