6/4 



CONCLUSION 



definite " adaxial " surface is presented towards it. It thus appears that the 

 most constant features of the embryo in Pteridophytes are: (i) the origin 

 of the axis in relation to the initial polarity of the embryo, and (2) the 

 orientation of the first leaves relatively to it. These facts once recognised 

 must needs take a premier place in Pteridophyte embryology. The 

 embryo is thus presented to the mind as consisting essentially of an axis 

 or spindle, liable in the different types to varying proportions of length 



FIG. 359. 



Diagrams of embryos : the suspensor is cross-hatched ; the hypobasal hemisphere 

 dotted, and the epibasal clear. A=Selaginella spinulosa. B = Selaginella Martensii. 

 C = Lycopodium Selago. D = Lycopodium clavatum. E Lycopodium cernuum. F 

 Isoetes. G Equisetum. H=Adiantum. c cotyledon ; ap apex of axis ; r root ; 

 Aj^ = hypocotyl; ;/=foot ; ,y = suspensor. These diagrams place various of the divergent 

 types described in the text in juxtaposition, and thus bring into prominence their points 

 of similarity and of difference. 



and breadth, upon which the other parts are inserted as appendages : 

 the leaves with a more regular relation, the roots with less regular 

 relation, and the haustoria or tubercles being occasional. In cases 

 where a suspensor is present this constitutes the organic base, while 

 the stem-tip forms the organic apex of the spindle, which is itself 

 built up from the suspensor, the hypobasal, and the epibasal tiers. In 

 cases where no suspensor is formed the relations of parts are still the 

 same, but the base is formed from the centre of the hypobasal tier; 

 often, however, the latter is specially developed as an haustorial foot, 

 or disguised by the early origin of a root. The spindle thus defined is 



