160 



PLANT BIOLOGY 



called dicotyledons (Greek, di = two + cotyledons). There are 

 other striking characteristics which distinguish these two groups of 

 angiosperms, which have already been brought out in our laboratory 

 work, as the following table will show: 



172. Plant families. Continuing our classification of the angio- 

 sperm group still further, we find that the dicotyledons are sub- 

 divided into over one hundred and sixty so-called plant families, 

 some of which are the violet family, the buttercup family, the rose 

 family, and the pulse family. This grouping into families is based 

 largely upon flower structure, and so it sometimes happens that 

 an herb and a tree belong to the same family. For example, the 

 pea, bean, and the locust tree all belong to the pulse family, since 

 they have flowers closely resembling each other. 



173. Plant genus. Again, each of the 160 or more families 

 is made up of a varying number of more closely related plant groups, 

 each of which is known as a genus. The rose family, for example, 

 has fourteen genera, some of which are the pear genus, the rose genus, 

 and the cherry genus. 



174. Plant species. Once more, each genus consists of a vary- 

 ing number of species, the members of which resemble each other 



