MORPHOLOGY 15 



distinctive differentiation of the Cormophyte is completed. This, 

 in all probability, has occurred twice in the phylogenetic development 

 of the vegetable kingdom ; once in the Bryophytes, and a second time 

 in the evolution of the Pteridophytes, presumably from ancestral 

 forms resembling the Liverworts. All Bryophytes are attached to 

 the surface on which they grow, by means of root-like hairs or 

 KHIZOIDS (Fig. 11, r). It is in the next higher group of plants, 

 which, as Vascular Cryptogams, are united in one class, that true 

 roots, in a morphological sense, first make their appearance. They 

 are for the most part cylindrical bodies with apical growing points. 

 Disregarding the distinctions perceptible in its internal structure, a 

 root may always be distinguished from a stem by the ROOT-CAP or 

 CALYPTRA sheathing its apex, and also by the absence of leaves. 



The Metamorphosis of the Primitive Forms. — After the completion 

 of its differentiation into stem and leaf, and the appearance of roots, 

 there occur only such modifications of the primitive form of the plant 

 body of a Cormophyte as are embraced under its metamorphosis 

 (p. 9), occasionally including a more or less complete fusion of parts 

 originally separate and distinct. 



The relationships between homologous members, which are often very striking, 

 did not escape the notice of earlier observers. They suggested comparisons, 

 although no real phylogenetic basis for such comparisons existed. Thus, an ideal 

 conception of the form of external members was developed, and finally reached 

 its highest elaboration in Goethe's Theory of Metamorphosis ; and its abstract 

 scientific conclusion in the writings of Alexander Bkatj n. As the great variety 

 exhibited in the external appearance of the lower plants precluded any possibility 

 of assigning to them hypothetical primitive forms, the whole terminology of the 

 external morphology of plants has been derived from conceptions applicable only 

 to the Gormophytes. Even to-day, the same terms used in reference to the 

 Cormophytes are applied to parts of the Thallophytes, which are evidently only 

 analogous. In this sense it is customary to distinguish between stem and leaf 

 in such Algae as Hydrolapathum (Fig. 9). Such a use of terms is only permissible 

 where reference is made to the manner of segmentation, with the intention of 

 emphasising the analogy with the somewhat similar members of the Cormophytes. 

 The question whether, in the different groups of the Cormophytes, all the members 

 designated by the same names are really homologous, cannot properly be discussed 

 here. It would seem almost impossible to derive from the Bryophytes all the 

 forms of cormophytic segmentation shown by the Pteridophytes. However this 

 may be, from the Pteridophytes upwards, the segmentation of the members appears 

 to have had a similar origin, and the similarity of terminology is based, therefore, 

 upon an actual homology of the parts. 



Relations of Symmetry 



Every section through an organ or member of a plant, made in 

 the direction of its longitudinal axis, is distinguished as a longitudinal 



