152 



MORPHOLOGY OF MEMBERS. 



(a) The conceptions of Stem, Leaf, Root, Trichome, as at present employed in botany, 

 result from the examination of highly developed plants, the different members of which 

 actually present considerable diversities, or display considerable differentiation ; but if the 

 attempt is made to apply these conceptions in the same manner to the less differentiated 

 Hepaticae, Algae, Lichens and Fungi, many difficulties arise, depending principally 

 on the fact that the members of the thallome sometimes display striking resemblances 

 to leaves, hairs, stems, and even roots, while wanting others of their characteristics. 

 Transitions occur from the members of Thallophytes which are but slightly differen- 

 tiated morphologically to the highly differentiated members of Gormophytes. In the 

 members which we term stem, leaf, root, hair, it is clear that those differences are 

 only augmented which 'also occur, though in a lesser degree, in the more homoge- 

 neous ramifications of the thallome, especially of the higher Algae; absolute distinctions 

 between thallomes and leaf-bearing axes are not to be found. It is therefore a matter 

 of convenience where the boundary-line is drawn. 



Fig. 115. — Longitudinal section through the apical region of three primary shoots of Charafragilis ; /the apical cell, in 

 which segments are formed by septa ; each segment being further divided by a curved septum into a lower cell which does 

 not further divide and which developes into an internode g s" s"'t and an upper cell which produces a node ?« m' and the 

 leaves. Each node-cell produces a whorl of leaves of different ages. (For a more exact description, see Book II, Characese.) 



(b) The expressions Thallome, Caulome, Phyllome, Trichome, Root, designate, as has 

 been said, general ideas, from the definition of which are eliminated all those properties 

 of the members which adapt them only for definite functions, while a few characters 

 only, drawn from their origin and mutual position, are kept in view. Parts which 

 are physiologically entirely different may therefore be morphologically equfvalent^ 

 and, vice 'versa, physiologically equivalent organs may fall morphologically under quite 

 different conceptions. The statement, for example, that the sporangia of Ferns are 

 trichomes, means only that they originate, like all hairs, from epidermal cells ; in this 

 characteristic hairs and the sporangia of Ferns are morphologically equivalent. On the 

 other hand the underground hairs of Mosses and the true roots of vascular plants are 

 physiologically equivalent ; both serve for the absorption of nourishment and the fixing of 

 the plant in the ground, although the former are morphologically trichomes, the latter 

 roots. 



