ROOT. i6g 



Ito the greatest extent morphologically and physiologically are connected by transi- 

 ftional 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. 



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 from 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. 



1 Compare the Hterature mentioned in the previous sections, and in addition, H. von Mohl, 

 Linnaea, 1837, p. 487.— Trecul in Ann. des Sci. Nat. 1847, vol. VIII. p. 268.— Peter- Petershausen, 

 Beitrage zur Entwickelungsgeschichte der Brutknospen. Hameln 1869.— Braun and Magnus, Ver- 

 handlungen des Bot. Vereins der Provinz Brandenburg, 1871 (on Crt///o/)s/s).— [Warming, Ramification 

 des Phanerogames ; Danish with French abstract. Copenhagen 1872.] 



