- ; C ) PHA NER GA MS. 



cambium-ring is then formed outside the one which has disappeared, and another one 

 again outside this one when it. has in turn disappeared. Several circles of fibro-vascular 

 bundles are thus formed, continually increasing in number. In many Menispermacex 

 (e-g. Gocculus), the new outer circle of vascular bundles together with its cambium-ring 

 is developed from a ring of meristem which lies in the primary cortex and therefore 

 outside the primary bast,— a phenomenon which is repeated in the primary cortex as 

 its growth proceeds (Nageli). In Phytolacca, on the other hand, and, according to 

 Eichler, also in Dilleniaceae, Bauhinia, Polygaleas (Securidaca and Comesperma), Cissus, 

 and Phytocrene, the successive circles of bundles originate in the secondary cortex. 

 Phytolacca agrees moreover with the cases mentioned under a in the primary bundles 

 lying also in the pith, and in the first closed ring which surrounds them being a secondary 

 production due to increase in thickness. 



Second Group. The secondary bundles arise early after the primary bundles further 

 inwards or nearer the axis of the stem (endogenous). 



a. Both the primary and the secondary endogenous bundles remain isolated ; they are 

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

 Nymphaeaceae and Papayer(?). The transverse section of the stem bears a greater or 

 less resemblance to that of a Monocotyledon, especially in Nymphaeaceee. 



6. 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 Piperaceae, Begoniaceac, and Aralia. 



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

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

 here. In Cucurbitaceae, some Solanacese, and Nerium (and in a certain sense also in 

 Tecoma radicam^, 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 Cucurbitacex. 

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

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

 to Sanio, Jlralia racemosa has an endogenous circle of closed fibro-vascular bundles 

 in which the xylem is outside and the phloem inside. The isolated bundles in the 

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

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

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

 of the inflorescence of Ricinus commuriis 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 Clasjification of Dicotyledo?is^ has now been carried out so completely that the 

 smaller groups which are called Families^, and w^hich 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 aflinity 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, Gamopetalai, and Eleu- 



' [See note to p. 553.] 



"^ Le Maout and Decaisne's Traits gs^n^ral de Botanique, descriptive et analytique, is strongly to 

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

 J873I. 



