630 PHANEROGAMS. 



decayed. This network of closely-placed closed fibro- vascular bundles now forms a 

 kind of secondary wood which surrounds like a hollow cylinder the space in which 

 the original fibro-vascular bundles of the stem run isolated and loose in the form of 

 long threads. This thickening ring of the arborescent Monocotyledons resembles 

 the secondary woody mass of Conifers and Dicotyledons in the fact that it belongs 

 altogether to the stem and has no genetic connection with the leaves, differing in this 

 from the original common bundles. An exception to the ordinary structure of Mono- 

 cotyledons occurs in submerged water-plants {Hydrilla and Potamogeton), in which, 

 according to Sanio (Bot. Zeitg. 1864, p. 223, and 1865, p. 184), an axial cauline bundle 

 in the stem lengthens continuously, while the foliar bundles do not unite with it till a 

 later period, a peculiarity which recurs in some dicotyledonous water-plants, and re- 

 minds one of the corresponding processes in Selaginella. 



The Systematic Classification ^ of the sub-sections of Monocotyledons here adopted is 

 that of A. Braun (in Ascherson's Flora of the province Brandenburg, Berlin 1864) ; but 

 with the variation that the order Helobiae there given is broken up into a series of 

 orders. In the short diagnoses of the orders only a few of the characters are specified 

 which are most important from a systematic point of view ; the figures placed within 

 brackets refer to those attached to the families belonging to the order in which the 

 characters named are present or absent. A complete account might have been given of 

 the characters of the separate families of Monocotyledons ; but since a similar treatment 

 of the class of Dicotyledons would have far exceeded our limits, the mere enumeration of 

 the families must, for the sake of uniformity, suffice. 



SERIES I.— Helobi^. 



Water-plants ; seed with little or no endosperm, but a strongly developed hypo- 

 cotyledonary axis to the embryo. The number of parts of the flower usually varies 

 from the ordinary type of Monocotyledons. 



Order i. CentrospermaB (so named from the central position of the seed in 

 (i) and in Naias). Flowers imperfect, very simple, usually without a perianth; in 

 (i) consisting of two stamens and a unilocular ovary (containing from i to 6 basilar 

 ovules) surrounded by a sheath (perianth or spathe) ; ovary in (2) unilocular, usually 

 one-seeded ; seed with but little endosperm. The Lemnaceae consist of small 

 branched leafless floating vegetating bodies, generally with true pendent roots; the 

 Naiadeae are slender branched long-leaved submerged plants; this family is not 

 definable systematically, and should be split up into several. (The Lemnaceae 

 should perhaps be united to the Aroideae.) 

 Families: i. Lemnaceae. 

 2. Naiadeae. 



^ [The systematic classification adopted in this book is not one v^hich the reader will find 

 followed in any standard English work, either as respects Monocotyledons or Die tyledons. The 

 work now generally adopted as containing the most satisfactory system of distribution of the vegetable 

 kingdom into classes, orders, and genera, is Bentham and Hooker's Genera Plantarum (London, 1862- 

 1873)^ which is however at present only completed so far as to include the Gamopetalse with 

 inferior ovary. In Dr. Hooker's edition of Le Maout and Decaisne's Traite Generale de Botanique 

 (London, 1873) will be found the outlines of this classification completed as far as relates to the 

 classes and orders. De Candolle's Prodromus Systematis Naturahs Vegetabilium in 1 7 vols. (Paris 

 1818-1873) contains a description of every known species of Dicotyledons; Walpers' 'Repertorium* 

 and 'Annales ' serving as supplements to the earlier volumes, which are far less complete than the 

 later ones. For an admirable epitome and illustrations of the character of each of the natural 

 orders see also Oliver, Illustrations of the Principal Natural Orders o-f the Vegetable Kingdom ; 

 London, 1874.] 



