XV] THE EMBRYO A SIMPLE LEAFY SHOOT 313 



The facts relating to the Ferns thus appear to be in general accordance 

 with the conception of the embryo as essentially of spindle-like, or even of 

 filamentous construction. The primitive spindle may be abbreviated by 

 elimination of its base, that is the suspensor. It may be further disguised 

 by cell-segmentation, and by lateral distension of the tissues thus formed. 

 The parts which it bears may vary in proportion and in some degree in their 

 apparent relations. But still there remains the fundamental fact of the 

 polarity of the spindle, which is established by the very first segmentation 

 of the zygote. InJ)oint of fact, the embryo of a Fern is a simple leafy shoot 

 from the first, and it may bear accessory suctorial organs, i.e. the foot and the 

 root : but neither of these is always present. 



The question remains how far the characters of the embryo thus con- 

 structed can be used in the phyletic treatment of the Filicales. If the 

 biological position of the embryo be constantly kept in mind, that will help 

 towards a just estimate of the value of the features of form and structure 

 which it shows. More especially is it important to remember how nearly 

 the embryo is dependent upon the gametophyte and its capacity for yielding 

 nutrition. The immediate point will be to distinguish between those features 

 which are directly plastic under present circumstances, and those which may 

 be held as inherited features common to the race and to its predecessors. 

 In an earlier phase of the science the majority of the features observed were 

 habitually ranked in the second category : at the present time the tendency 

 is to give full latitude to the former, recognising a high degree of adaptability 

 in the young embryo. With criticism illuminated by such ideas as these, 

 there are four lines of comparison that may be traced from the study of 

 embryos, which may be used in the phyletic treatment of the Filicales. 

 They will be considered in succession. 



(i) The most constant character of the embryo of the Filicales is its 

 polarity, which is expressed with varying clearness in the spindle-form. Bu-t 

 this is liable to be masked by the elimination of the base of the primitive 

 spindle, which we call the suspensor. Those embryos which have a suspensor 

 may be held to retain their primitive state more fully than those which have 

 none. In fact the suspensor is held to be an archaic feature. Nevertheless 

 the recognition of this must not be pressed too far. It may be retained as 

 a vestigium in cases which are not primitive in other features. For instance, 

 because Danaea has a vestigial suspensor and Angiopteris has none, it does 

 not follow that Angiopteris is a more advanced Fern than Danaea, though 

 it has lost this archaic feature. The spindle-structure is further obscured by 

 transverse distension, especially seen in the epibasal and hypobasal regions. 

 This is manifest in the embryos of the Marattiaceae (Fig. 286), and in those 

 of Ophioglossum vulgatum and Botrychium Lunaria (Figs. 292, 293). In all 

 of these the hypobasal and epibasal hemispheres are so dilated laterally that 



