48 NATTJKB OF VEGETABLE FAMILIES. 



THE FAMILIES OF BLANTS. 



A family of plants comprehends all those in a given class and 

 section which are intimately alike in their general structure, and 

 usually have a striking outward likeness in addition. The members 

 are referable, for the most part, to some well-marked vegetable type, 

 and seem to cluster, as to their characters, round a particular species 

 which concentrates the natures of all. This central or concenti-ative 

 species is used as the vame for the family. The " Buttercup-family" 

 is that of which the buttercup is representative ; the " Cabbage-family" 

 that of which the garden cabbage is the type, and so v/ith all the 

 others. The exact boundaries of the several families are sometimes a 

 little uncertain, because on the confines they are prone to mingle, like 

 the natives of contiguous countries. For the true idea of them we 

 must look, accordingly, to the centre, determining them not so much 

 by what they strictly exclude, as by what they obviously and uumis- 

 takeably mclude. But it must not be thought that all the members 

 of a family resemble the typical species in colour, bulk, and stature. 

 Trees and herbaceous plants, land-plants and aquatics, may all be 

 comprised in the same family ; differences of size, colour, and place of 

 growth being accidents compatible with completcst resemblance as to 

 essentials. The concurrence as to general properties among the mem- 

 bers of a family was mentioned some pages back. There is an agree- 

 ment also in the very nature of the sap. Trees of the same family 

 graft readily with one another, but those of different families are 

 indisposed to unite, even if they do not absolutely refuse, shewing at 

 once which of a large company are aliens, and which have real 

 afl&nity. The plants of the Ash-tree-family and those of the Jessa- 

 mine-family were once thought nearly related; but although the 

 former are somewhat heterogeneous, they graft readily on each other's 

 branches, while the latter, which they resemble superficially, refuse 

 to combine with them. 



The families of plants vary greatly in extent. Some contain but 

 half-a-dozen species ; others many thoiisands ; their own numbers, so 

 far as ascertained, ])cing about 300. They are seldom confined to a 

 single country, but spread all over the world, though more plentifully 

 in some latitudes than others, according as they are fond of heat or 

 cold. The chief part belong to the tropics, but some are almost 

 entirely extra-tropical. It is curious to sec how families eminently 

 belonging to warm countries, such as the mallow-tribe, creep, in a few 



