NATURAL ORDERS. 1XXV 



V. ARRANGEMENT OF THE NATURAL ORDERS IN/THE 

 PRESENT WORK. 



The very unequal manner in which the several Natural Orders are 

 represented in the British Isles renders it impossible, in a work con- 

 fined to British Plants, to give any fair idea of the subclasses into which 

 these Orders have been grouped, or of the principles which have guided 

 the authors of the linear arrangement the most generally followed. The 

 following recapitulation is therefore merely intended as a sort of table 

 of contents, showing the order in which the families follow each other 

 in the present work ; at the same time that the attention is called to 

 one or two of the most striking, the most important, or the easiest ob- 

 served features of each one. These characters are, however, general, 

 not always without exception, and sometimes specially applicable to 

 British genera only. 



CLASS L DICOTYLEDONS. 



In the germination of the seed the plumula arises between two (rarely 

 more) lobes or cotyledons of the embryo, or from a terminal notch. [The 

 vascular tissue of the stem forms a ring or rings between the bark 

 and pith. The nerves of the leaf are branched and netted (see also 

 Arum, Tamus and Paris in Monocotyledons). The parts of the flower 

 are usually in fours or fives.] 



Subclass 1. THALAMIFLORJE. Petals distinct from the calyx, and 

 from each other, seldom wanting. Stamens usually hypogynous, or 

 nearly so. [Exceptions. The calyx or corolla is absent in some Ranun- 

 culaceae, Cruciferae, Violaceae, Caryophyllaceae. The petals cohere more 

 or less in some Fumariaceae, Polygalaceae, Portulaceae, Tamariscineae, 

 Malvaceae. The stamens are epigynous or perigynous in Nymphaeaceaa 

 and some Caryophyllaceae.] 



* Ovary apocarpous. 



I. Ranunculaceae. Petals definite. Stamens indefinite. 



II. Berberideae. Perianth and stamens in twos or threes, or their 

 multiples. Anthers opening by recurved valves. 



III. Nymphaeaceae. Aquatic plants with indefinite petals and sta- 

 mens, the inner petals passing gradually into the outer stamens. 



** Ovary syncarpous. Placentas parietal (except in Polygalaceae). 



IV. Papaveraceae. Perianth regular, in twos or fours. Stamens in- 

 definite. 



V. Fumariaceae. Perianth very irregular, in twos or fours. Stamens 

 6, in two sets. 



VI. Cruciferae. Sepals and petals 4 each. Stamens 6, of which 2 

 shorter. 



VII. Resedaceae. Petals small, unequal, some divided. Stamens few 

 but indefinite. Capsule open at the top before it is ripe. 



VIII. Cistaceae. Sepals 3, equal, or with additional small ones. Petals 

 5, regular. Stamens indefinite. 



IX. Violaceae. Stamens 5; the anthers on the inner face of very 

 short broad filaments, usually united in a ring. Capsule 3-valved. 



