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 Cormophytes. 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 Algse; 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 vi'hich does 
not further divide and which developes into an internode g g" g'", and an upper cell which produces a node m in' and the 
leaves. Each node cell produces a whorl of leaves of ditfetent ages. (For a more exact description, see Book II, CharaceEC.), 
(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 equi'valentj 
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. 
