22 THE PHENOMENON OF 



as essential part of the sprout, has its history of develop- 

 ment intimately connected with that of the stem ;* on 

 the other hand the formation of the sprout does not 

 seem to have any essential connection with the com- 

 pletion of the stem from which it proceeds. This is 

 further confirmed by the circumstance that the sprouts 

 are not always distributed, like the leaves, in definitely 

 regulated order on the stem, but in many cases may 

 arise without order at any points of herbaceous stems, f 

 or of the older lignified trunk, nay even from the rootj 

 and the leaf, as the so-called adventitious buds. 



It is a remarkable indication for the essential dis- 

 tinction in the origin of the leaf and sprout, that no 

 adventitious leaves occur. The character of the newr 

 formation is expressed most distinctly in the formation of 

 adventitious buds making its appearance in detached 

 fragments of roots of woody plants, as has been described 

 byTrecul mAilanthus, Pauloionia, Tecoma, and Ifaclura. 

 Here, in a deep-seated layer of the cellular bark, a new 

 focus of development is formed through a local thicken- 

 ing of the cellular tissue, and on this point again origi- 

 nates a much more delicate mass of cellular tissue, a new 

 sphere of formation, which soon grows externally, al- 

 though still enclosed in the tissue of the bark, into a 

 leaf-producing point of vegetation, and on the inside 

 strikes, stem-like, into the formative zone (the cam- 

 bium-layer) of the root, there, by the formation of a 

 proper system of vessels, which takes its origin on the 

 limit between the stem of the adventitious bud and the 

 wood-cylinder of the root, acquiring a firm connection 



* Tlie essential interconnection of the leaf and stem is expressed in the 

 completed structure also, in the fact that there is no sharply defined limit 

 between the leaf and the portion of stem bearing it. Remark, for instance, 

 the pulvini gradually lost in the stem of Laria; Ficea, Cactece, Cacalia 

 articnhda, &c., and stems winged by the deourrenoe of the borders of leaves. 



f In Euphorbia, Linaria, and Anagallis, from the internodc Ijelow the 

 cotyledons. 



% Frequently in woody, rarely in herbaceous plants, e. g. Hiiporhia Ci/par- 

 issias, Linaria, Rumex acetosella, Ajugu geuevensis, Naxliirliinn pyrenuieum, 

 Juriiiea PnUichii, KaA Ilelichrj/svm arenariiim . 



