ROOT. 
169 
to the greatest extent morphologically and physiologically are connected by transi- 
tional forms, and that, especially in the branched thallomes of Algae, the rudiments 
are to be found of all the differentiations of the higher plants. Distinctions which, in 
the ramifications of the Alga-thallus, are only of a weak, undefined, and rudimentary 
character, increase more and more in the higher plants; points which can be sharply 
defined in the latter become indistinguishable when we are considering the more simple 
Thallophytes. The more the attempt is made to establish exact definitions for single 
forms, the more does one become convinced that all definition, all limitation, is arbi- 
trary, and that Nature presents gradual transitions from the indistinguishable step by 
step to the distinct, and finally to the opposite. 
Sect. 24. Different Origin of Equivalent Members ^ — (i) The different 
members of a plant spring out of one another ; the members produced may there- 
fore be similar (homogeneous), or dissimilar (heterogeneous) to the member which 
produced them. In the former case the formation of new members is ordinarily 
termed Branching ; in the latter it is regarded as the production of a new member. 
A root, for instance, branches in the production of new roots, a stem in that of new 
stems, a thallome in that of new thallomes ; in the same sense the production by a 
leaf of lateral leaf- structures must also be considered a case of branching. On the 
other hand the stem produces also leaves, roots, and hairs ; leaves not unfrequently 
produce leaf-bearing shoots, sometimes roots, generally hairs; leaf-forming buds may 
also arise from roots. But since members which are morphologically dissimilar — 
stem, leaf, root, trichome — do not differ absolutely, but only in degree, the difference 
between branching and the production of new members, between homogeneous 
and heterogeneous growth, must be regarded not as an opposition, but only 
as a gradually increasing differentiation of the members which grow out of one 
another. 
(2) New members may originate either by Lateral Budding or by Dichotomy. 
Lateral budding occurs when the producing member, after its previous increase in 
length at the apex, forms outgrowths below it, which are from the very first weaker 
than the portion of the axial structure which lies above them. Dichotomy, on the 
other hand (rarely Polytomy), is caused by the cessation of the previous increase in 
length of a member at its apex, and by two (or more) new apices arising side by 
side at the apical surface, which, at least at first, are equally strong, and develope in 
diverging directions. Lateral budding may either form structures which are similar or 
dissimilar to the axial structure ; and thus leaves, roots, hairs, or branches arise by 
lateral budding frorj^i the stem; leaflets, lobes, hairs, sometimes leaf-bearing shoots, 
or even roots, from the leaf. Dichotomy, on the contrary, never produces struc- 
tures which are dissimilar to the producing structure ; the divisions of a root 
produced by dichotomy are both roots, those of a leaf-bearing shoot both leaf- 
bearing shoots, those of a leaf both foliar structures ; dichotomy hence always falls 
under the conception of branching in the above-named narrower sense. 
^ Compare the literature mentioned in the previous sections, and in addition, H, von Mohl, 
Linngea, 1837, p. 487. — Trecul in Ann. des Sei. Nat. 1847, vol. VIII. p. 268. — Peter -Petershausen, 
Beiträge zur Entwickelungsgeschichte der Brutknospen. Hameln 1869. — Braun and Magnus, Ver- 
handlungen des Bot. Vereins der Provinz Brandenburg, 1871 (on Calliopsis). — [Warming, Ramification 
des Phanerogames ; Danish with P'rench abstract. Copenhagen 1872.] 
