654 ^^^^ NEROGA MS. 



o. Both the primary and the secondary bundles remain isolated ; they are not 

 united by a closed cambium-ring, but anastomose with one another, as in Cucurhita, 

 Nympha^aceac, and Papaver. In the Gucurbitaceae and Piperaceae the more internal 

 bundles are arranged in a ring, but in the Nymphaeaceae they are arranged irregularly, 

 so that the transverse section of the stem bears a greater or less resemblance to that 

 of a Monocotyledon. 



b. The primary bundles lie in a ring on the transverse section, and are united by 

 a cambium-ring ; the secondary bundles arise at an early period in the pith and remain 

 isolated and scattered on the transverse section ; they anastomose with one another and 

 with the primary bundles in the nodes of the stem. Examples are furnished, according 

 to Sanio, by Begoniaceae, Aralia, and some Umbelliferae. 



The Cell-forms of the phloem and xylem of Dicotyledons have already been described 

 in general terms (see p. ii6 et seq.). Only two peculiar phenomena need be mentioned 

 here. In Gucurbitaceae, some Solanaceae, and Nerium (and in a certain sense also in 

 Tecoma radicans^), a phloem-tissue is found not only on the outside but also on the inside 

 of the fibro-vascular bundles, which is developed with especial strength in Gucurbitaceae. 

 The isolated fibro-vascular bundles in the pith which are enclosed by the ring of wood 

 sometimes show an abnormal arrangement of their phloem and xylem. Thus, according 

 to Sanio, Aralia racemosa has, within the normal circle which grows by means of a 

 cambium-layer, an endogenous circle of closed fibro-vascular bundles in which the xylem 

 is peripheral and the phloem central as regards the stem. The isolated bundles in the 

 pith oi Phytolacca dioica on the other hand consist, according to Nageli, on a transverse 

 section, of a hollow woody cylinder which surrounds the phloem on all sides and is 

 penetrated by xylem-rays. The isolated fibro-vascular bundles of the pith in the rachis 

 of the inflorescence of Ricinus communis also consist of a thin axial bundle of phloem (?), 

 surrounded by a sheath of cells (xylem ?) arranged in rays. 



A layer of collenchyma is very common in Dicotyledons beneath the epidermis of 

 the internodes and leaf-stalk. 



The Classificat'tGn of Dicotyledons ^ has now been carried out so completely that the 

 smaller groups which are called Families ^, and which usually comprise genera very 

 nearly related to one another, have been united into larger groups or orders ; so that 

 at present only a few families remain unplaced. The greater number of the orders can 

 also be again arranged into larger groups which are clearly connected by actual relation- 

 ship. Systematists have not however up to the present time agreed as to how many of 

 these cycles of affinity should be established, so as to make the primary division of the 

 whole class of Dicotyledons in accord with the requirements of scientific classification. 

 The grouping of all Dicotyledons into three sections, Apetalae, Gamopetalae, and Eleu- 

 theropetalae, proposed by De GandoUe and Endlicher"^, ic now abandoned by most, 

 although still much in use for practical purposes. A. Braun^ placed among the Eleu- 

 theropetalae the greater number of plants previously classed among Apetalae ; and 

 Hanstein^ has now distributed among them the remainder, so that the whole class 

 consists of only two sub-classes, Gamopetalae and Eleutheropetalae. This classifica- 



* [A cambium-ring is formed internally to the primary bundles in the stem of this plant ; see 

 Nageli, Beitrage, I : also Sanio, Bot. Zeitg. 1864, p. 228.] 



^ [See note to p. 630.] 



^ Le Maout and Decaisne's Traite general de Botanique, descriptive et analytique, is strongly to 

 be recommended for a study of the diagnosis of the families [translated by Mrs. Hooker; London 



1873]. ^ 



* Endlicher, Genera plantarum secundum ordines naturales disposita, Vindobonae, 1836-1840; 

 and Enchiridion botanicum, Lipsiae — Vienn^e, 1841. 



•'"' A. Braun, Uebersicht des naturlichen Systems, in Ascherson's Flora der Provinz Brandenburg, 

 1864. 



•^ Hanstein, Uebersicht des natlirlichen Pflanzensystems, Bonn 1867. In the first edition of this 



