THE PAST HlSTOIiY OF PLANTS. 223 



in other respects as widely from its neighbours 

 as gorse and clover, peas and laburnum, broom 

 and vetches, scarlet-runners and lupines. A 

 group of kinds, so derived from a common pro* 

 genitor, but preserving throughout one or more 

 of that progenitor's peculiarities while differing 

 much in other respects among themselves, is 

 called a family. Thus we speak of the family 

 of the peaflowers, the family of the roses, the 

 family of the lilies, the family of the orchids. 

 Each family may include several minor groups, 

 Jmown as genera (in the singular, a genus) ; and 

 each such genus may further include several 

 distinct kinds or species. 



For example, all the peaflower family are dis- 

 tinguished by their possession of a peculiar 

 blossom whose corolla consists of a standard, a 

 keel, and two wings, like sweet-pea or broom. 

 This family contains several genera, one of 

 which is that of the clovers, including certain 

 peaflowers which have learned to mass their 

 blossoms into a roundish head, and have trefoil 

 leaves, and very few seeds in the short seed-pod. 

 The clovers, again, are subdivided into species or 

 kinds, such as purple clover, Dutch clover, hop 

 clover, and hare's foot clover ; in Britain alone, 

 we have twenty-one such distinct species or 

 kinds of clover. You will see at once that this 

 method of grouping by ancestral forms enables 

 us largely to reconstruct the history of each 

 particular plant or animal. 



Why don't these kinds cross freely with one \ 

 another, and so produce an endless set of 

 puzzling hybrids ? Well, they do occasionally ; J 



