WHAT IS A SPECIES? 143 



merely assemblages of individuals agreeing between 

 themselves in certain important particulars which 

 separate them from other groups which have other 

 particulars in common. The question. What is a 

 species ? can be illustrated more easily than it can 

 be denned. Thus all plants may first be divided 

 into two leading groups, those which produce true 

 flowers and seeds and those which do not. The 

 flowering plants may then be divided into those 

 having solid, woody stems and a true bark, and 

 those which have hollow or pithy stems without 

 solid wood, and are destitute of bark Among the 

 ordinary woody plants may be found some having 

 the petals of their flowers more or less united into 

 a tube, and others with their petals wholly distinct. 

 In the latter group are certain kinds which attract 

 attention by their compound leaves, and by having 

 flowers with one broad petal which stands up above 

 the others, and which produce a peculiarly flattened 

 pod. Many plants, differing in other particulars, 

 have these three characters in common; in short, 

 they exhibit a family likeness, and the group taken 

 together is called the pea or bean family. In this 

 and other families are subordinate groups, called 

 genera, and in each genus still smaller groups, 

 known as species. These various groups, one 

 within another, were discovered and named for the 

 most part ; before the present belief in the origin of 



