ANGTOSPERMS. — D/COT] LKDONS. 467 



found on the inside, and this is especially developed in the Cucurbitaceae ; such 

 vascular bundles are termed bicollaicral. 



The isolated bundles in the pith which are surrounded by the wood-cylinder some- 

 times show an abnormal arrangement of the phloem and xylem. Thus in Aralia 

 raceinosa according to Sanio, inside the outer circle which is constantly forming from 

 a cambium-ring, there is an internal (endogenous) circle of closed bundles, in which the 

 xylem is towards the periphery and the phloem towards the axis of the stem. The 

 isolated bundles in the pith of Phytolacca dicnca on the other hand according to 

 Nageli consist on the transverse section of a hollow cylinder of xylem, which entirely 

 surrounds the phloem and is itself pierced by xylem-rays. 



A layer of collenchyma beneath the epidermis of the internodes and leaf-stalks is 

 very common in Dicotyledons. 



The classification of Dicotyledons is now so far completed that the smaller groups 

 known as families ', which usually embrace nearly allied genera, are united into 

 larger groups or orders, and few families still remain unplaced. The greater number 

 of the orders may also be collected into more comprehensive groups evidently bound 

 together by real affinity. Botanists however are not yet agreed as to how many 

 of these cycles of affinity must be established, and what must be the primar}-^ divisions 

 of the whole class in accordance with the requirements of a scientific classification. 

 The arrangement of Dicotyledons by De Candolle and Endlicher'- into three divisions, 

 Apetalae, Gamopetalae and Choripetalae, is now pretty well given up in theory, though 

 still often used in practice. A. Braun has placed the greater part of the Apetalae 

 with the Choripetalae, and J. Hanstein has found room there for the remainder, so 

 that the class has now only two sub-classes, Gamopetalae and Choripetalae. Eichler 

 has also retained this arrangement in his syllabus, which will be followed in the present 

 enumeration of the several groups with some slight alterations, as was done in the 

 case of the Monocotyledons. The two primary groups of the Dicotyledons therefore 

 are the Choripetalae with free separate petals, or without a corolla (formerly the 

 Apetalae), and the Gamopetalae''' with a tubular or bell-shaped corolla with free teeth 

 at the margin. 



A. CHORIPETALAE. 



I. Jviliflorae. 



Very small inconspicuous flowers crowded in compact inflorescences, spikes, capitula, 

 more rarely panicles, often of very peculiar form. Flowers naked or surrounded by 

 a calyx-like perianth (not differentiated into calyx and corolla), usually diclinous, male 

 and female often different ; leaves simple. 



Order i. Amentaceae : Flowers unisexual, in contracted panicles (false spikes), 

 the female inflorescence with few flowers, surrounded with a cupule in Cupuliferae ; 

 ovary inferior; fruit one-seeded, dry indehiscent without endosperm. Trees with 

 deciduous stipules. 



Families : I. Betuleae, 4. Salicineae, 



2. Cupuliferae, 5. Casuarineae. 



3. Juglandeae, 



1 [See note on p. 443.] The Traite general de Botanique descriptive et analytique par E. le 

 Maout et J. Decaisne, Paris, 1876 (English Edition by Sir J. D. Hooker), is to be recommended for 

 the study of the characters of the families. See also Eichler, Bliithendiagramme, I and II. 



2 Endlicher, Genera plantarum secimdum ordines naturales disposita, Vindobonae, 1836-1S40 ; 

 and Enchiridion botanicum, Lipsiae-Viennae, 1 841. 



» Also recently and fitly termed Sympetalae (see Eichler, loc. cit.) ; the expression is apt, because 

 the gamopetalous corolla is not the result of a cohesion of originally free parts, but is due to excessive 

 growth of the zone of the floral nxis in which rudiments of the petals are inserted. The term 

 Gamopetalae may however be retained as a figurative expression. 



H li 2 



