INTRODUCTION. lv 



form or other, and bulbs are a usual character of Asphodeleae and Amaryl- 

 lideae ; in the former, however, the bulb is often represented by a rhizoma, 

 orcormus, as in Brodiaea, Leucocoryne, and their allies, or by those succu- 

 lent fibres called fasciculate roots, as in Asphodelus itself; and in the latter 

 the bulb is sometimes entirely absorbed by succulent perennial leaves, as 

 in Clivia. 



External variations in the figure of the stem are sometimes available 

 as distinctions of orders. Thus, a twining stem is almost without excep- 

 tion in Menispermese, a square stem is universal in Labiate, and an angular 

 oneinStellatie ; but more frequently its figure affords no indication whatever 

 of affinities. — Texture of the stem is of scarcely more value. Cacteac, it 

 is true, have always the cellular tissue in excess, and derive by that circum- 

 stance one of their great distinctions from Grossulaceae ; but even in Cacteae 

 the Pereskias are scarcely more succulent than other plants ; and Euphor- 

 biacere and Asclepiadeae exhibit instances both of the most decided slate of 

 anamorphosis, and of the normal condition of stems in general. — In the 

 internal arrangement of the layers of Exogenous stems, I am not aware 

 of any character which distinguishes orders besides those to which I have 

 already adverted ; except in Calycantheae, which are distinctly known by 

 the presence of four incomplete centres of vegetation surrounding the 

 principal one, and so forming four angles which are visible externally. 

 (See MirbeFs figure, in the Annales des Sciences, vol. xiv. p. 367.) But 

 as I have before observed, very little is really known upon this subject. 



The Leaves are subject to modifications not less important in deter- 

 mining the mutual relations of plants, than the functions which they 

 perform in the vegetable economy. Their characters depend upon their 

 relative position, their degree of division, their venation, and the presence 

 or absence of pellucid dots within their substance. — All Cinchonacese 

 (Rubiaceae) have opposite entire leaves ; in Labiatee, Apocyncse, Gentia- 

 neae, Monimieae, and many others, they are also uniformly opposite ; but 

 in the genus Fuchsia, in which they are usually opposite, species exist 

 in which they are not only alternate, but both the one and the other on 

 the same plant ; and alternate-leaved species exist in Compositae, Scro- 

 phularineae, and Malpighiaceae, orders the leaves of which are generally 

 opposite. In Cupuliferae, Umbelliferae, Ternstisemiaceae, Hamanielideae, 

 and Urticea?, they are uniformly alternate ; but in Combretaceae and 

 Leguminosae, orders usually having alternate leaves, they are occasionally 

 opposite ; and Haloragea?, Ericinea?, and Ficoidea?, are orders in which 

 the genera have their leaves arranged in no certain manner. I do not 

 know how far this irregularity is connected with the following observa- 

 tions of Schlechtendahl, which, however, deserve attention. " Those 

 leaves," he says, " which are connected either by their base, or by the 

 intervention of a stipula, I call opposite, and those which are not so con- 

 nected, spuriously opposite (pseudo-opposita). Opposite leaves are never 

 disjoined, as in Rubiaceaj and Caryophyllere ; spuriously opposite ones, 

 which are much more common, being easily disjoined, readily become 

 alternate. Branches obey the same laws as leaves." Linncca, 1. 207. — 

 All Spondiaceae, Rhizoboleae, &c, have compound leaves ; in many others 

 they are always simple; and in such orders as Acerineae, Aurantiaceae, 

 Geraniaceae, Rutaceae, and Sapindaceae, both simple and compound leaves 

 are found. This character, therefore, is not considered of so much value 

 as many others. — Neither is the degree of division of the margin usually 



