NATURAL SYSTEM. 175 



2-cleft ; fruit 4 separate akaines around the base of the style, loose 

 in the calyx and resembling naked seeds. 



We examine the stem ; it is herbaceous, tetragonous (4-angled, 

 square) ; the leaves are simple, opposite ; the whole plant is aromatic. 

 At every step we find plants resembling the Sage: -Basil, Lavender, 

 Mint, Pennyroyal, Thyme, Catnip, Hoarhound ; sometimes with 2 

 stamens, many times with 4 didynamous ones, but always with the 

 same fruit. The plants are never trees, very rarely shrubs. They are 

 grouped with the Sage, and called Labiatm. 



424. Orders. — When Jussieu completed the Natural 

 Method there were only 100 known Orders. Since 

 that time discoveries have greatly increased the number; 

 yet all the Orders, Genera, and Species are so carefully 

 grouped that a few thousand words serve to name them. 

 The study of relationships had led the later botanists — 

 Le Maout and Decaisne, Lindley, Hooker, and Bentham 

 — to break up some Orders and redistribute their Genera, 

 or to unite several Orders into one. Jussieu regarded 

 apetalous and diclinous flowers as arrested conditions of 

 perfect types, which masked affinities without annulling them. 

 The student will thus account for the occasional placing of 

 such forms among perfect types, — such as the Ash with the 

 Olive, the Meadow-Rue with the Buttercup ; also the Nut>- 

 meg Order near that of the Magnolia. In the Manual (at 

 the end of this volume) the Orders are grouped into Alli- 

 ances, after the method of Lindley, but following Jussieu's 

 sequence. It is not easy to settle the relationship of some 

 Orders ; these doubtful ones are marked with an asterisk. 



425. Sub-Orders, Tribes. — In some Orders the plants 

 differ in so many respects that they are separated into Sub- 

 Orders, and these again into Tribes ; Genera, too, have 

 Sub-Genera, or Sections. For example : In the Order 

 Leguminosce (Pea) the common characters which link its 

 genera into one family are a free simple ovary, embryo 

 without perisperm, and fruit a legume, or loment. Yet 

 there are such differences in their stamens, petals, and 

 habits that they have been separated into 3 Sub-Orders, — 

 viz. : 1. Papilionacese (Peas) ; 2. CsesalpinesB (Logwoods) ; 

 3. Mimoseee (Mimosas) ; each Sub-Order being named 

 after its representative type. The Genera of each Sub- 

 Order have likewise some common trait ; but they differ 

 in other characters, and are therefore separated into Tribes, 



