44 INTRODUCTION. 



Oxygen in greater excess than in Water. 



Vegetable Acids. These possess the usual properties of the mineral acids, 

 being sour, reddening vegetable blues, .and forming salts with bases. Some 

 of them, however, have the power of uniting with more than one atom of 

 base, and hence are called polybasic; by heat, they are frequently resolved 

 into more simple acids. Some of them are very generally diffused through 

 the vegetable kingdom, whilst others are confined to one or more orders. In 

 general they contain no nitrogen. 



CLASSIFICATION OF PLANTS. 



Systematic Botany has been defined by Dr. Lindley, to be " the science of 

 arranging plants in such a manner that their names may be ascertained, their 

 affinities determined, their true place in a natural system fixed, their sensible 

 properties judged of, and their whole history elucidated with certainty and 

 accuracy." To accomplish this, all botanists, whatever might be their views 

 as to the mode and order in which the members of the vegetable kingdom 

 were to be arranged, have felt the necessity of separating them into groups, 

 which they divide and subdivide in various ways, in accordance with their 

 respective views. At the present day, the following divisions are universally 

 adopted, though there is some difference of opinion as to the exact limits of 

 some of them. 



A Species includes all individuals which, although they may differ in un- 

 important particulars, are identical in their real characteristics, and produce, 

 from their seeds, other plants wholly resembling the parent. When slight 

 differences occur in these offspring, as a variance in the colour, &c. ; they 

 are called varieties. 



A Genus is a group of closely-related species, agreeing more with each 

 other in their characters than with plants of another group. When some of 

 these are more closely allied together, than with others of the genus, they 

 have been erected into a sub- genus. 



An Order, or Family, is a group of nearly-connected genera, and where 

 certain minor groups exist in it, they are said to constitute a sub-order. Some 

 botanists are of opinion that it is advantageous to consider the different groups 

 into which a sub-order may be divided, under the name of Tribes, which they 

 again separate into sub-tribes. 



A Class, is a group of orders having certain marked characters in common. 

 This, in like manner with the other divisions, is separated into sub-classes. 



An enumeration of the points of difference or distinguishing marks of any 

 one of these groups, whether of higher or lower order, is denominated its 

 character. Thus the character of a class points out only those important 

 points of structure on which it is founded; that of orders, notices the general 

 structure of the plants embraced in it, especially of their fruit and flowers ; 

 the generic character, the particular modifications of the ordinal character in 

 a given genus ; and lastly, the specific character gives those less important of 

 form, colour, &c, which mark it as distinct from its kindred. 



Two methods of arranging plants have been followed ; one the Artificial, 

 founded by Linnreus, and at one time almost universally followed by botanists; 

 the other, the Natural, originally sketched out by Jussieu, and since improved 

 and augmented by the researches of many eminent botanists. The first of 

 these has no other merit, nor was any other proposed by its author, than that 

 of furnishing a ready mode of ascertaining the name of a plant, its rela- 



