314 THE EMBRYO [CH. 



it is only by comparison, and by their further development, that it becomes 

 apparent that the axis of organisation cuts the basal wall at right angles. 

 These features, combined with the early formation of the appendages, have 

 disguised the spindle-construction of the embryo, so that in many Ferns it 

 is only recognised with difficulty. 



(2) A second feature is the cellular segmentation of the embryo. In 

 certain Ferns the embryo is relatively massive with less definite segmentation: 

 in others it is less massive with more exact segmentation. This runs naturally 

 parallel with the like differences of segmentation of the several parts as 

 compared in Chapter VI. It was there concluded that the less definite 

 segmentation is characteristic of the more massive and relatively primitive 

 types, and the more definite of the delicate and relatively derivative types. 

 The former is seen in the embryos of the Eusporangiate, the latter in those 

 of the Leptosporangiate Ferns (Figs. 286, 294). This accords with the facts 

 relating to the suspensor, which is retained only by certain Eusporangiatae, 

 and is always absent from the Leptosporangiatae. On both grounds the 

 former are thus indicated as relatively primitive, and the latter more advanced 

 types. 



(3) A third feature lies in the relations of the primordial organs to the 

 basal wall. In all Ferns the axis and cotyledon arise from the epibasal 

 hemisphere. In many of the Eusporangiates the first root also springs from 

 it, and in others it arises about the border line. But in all the Leptosporan- 

 giates it arises from the hypobasal hemisphere. This is held to be a later 

 and derivative state. The foot, or haustorium, where present, arises univer- 

 sally from the hypobasal hemisphere. 



(4) Certain embryos are characterised by delay, or even suppression of 

 the development of certain parts. In Botrychinm Lunaria the first leaves 

 appear only as scale-leaves, and it is stated that about the eighth of them 

 is the first leaf to appear above ground. In Ophioglossum mohiccanum and 

 pedimculosnm the apex of the axis is arrested ; it appears from the descrip- 

 tions to be replaced later by an adventitious bud on the root. In Salvinia 

 no root is formed, but the whole hypobasal region develops as a foot. All 

 of these departures from the normal numbers and relations of parts may be 

 held as secondary; i.e. derivative from that recognised as normal. They 

 may all be explained as biological adaptations. 



It may finally be asked what weight is to be accorded in our general 

 comparison of the Filicales to the facts of the primary embryogeny. Its 

 details have been highly estimated in the past, and sometimes they have 

 been made the basis for far-reaching conclusions. A bias towards this may 

 have originated from the success of the recapitulation-theory in Animal 

 Morphology, and this has no doubt influenced botanical opinion. But how- 

 ever convincing the analogies between the two kingdoms may appear to 



