THE VARIOUS FORMS OF PLANTS 157 



sexual or asexual growth, and the stage of asexual growth is usually- 

 separated from the period of sexual growth. 



Systematic Botany. — The plant world is divided into many 

 tribes or groups. And not only are plants placed in large groups 

 which have some very conspicuous characters in common, but 

 smaller groupings can be made in which perhaps only a few plants 

 having common characters may be placed. If we plant a number of 

 peas so that they will all germinate under the same conditions of 

 soil, temperature, and sunlight, the seedlings that develop will each 

 differ one from another in a slight degree. But in a general way 

 they ■«'ill have many characters in common, as the shape of the 

 leaves, the possession of tendrils, form of the flower and fruit. 

 The smallest group of plants or animaU having certain characters in 

 common that make them different from all other plants or animals is 

 called a species. Individuals of such species differ slightly; for 

 no two individuals are exactly alike. 



Species are grouped together in a larger group called a genus. 

 For example, many kinds of peas — the garden peas, the wild 

 beach peas, the sweet peas, and many others ■ — are all grouped in 

 one genus (called Lathyrus, or vetchling) because they have certain 

 structural characteristics in common. 



Plant and animal genera are brought together in still larger 

 groups, the classification based on general likenesses in structure. 

 Such groups are called, as they become successively larger. Family, 

 Order, and Class. Thus the whole plant and animal kingdom is 

 grouped into divisions, the smallest of which contains individuals 

 very much alike; and the largest of which contains very many 

 groups of individuals, the groups having some characters in com- 

 mon. This is called a system of classification. 



Classification of the Plant Kingdom. — The entire plant king- 

 dom has been grouped as follows by botanists : — 



, „ , , , [ Angiosperms, true flowering plants. 



1. Spermatophytes. \ ^ x. • j xi, • n- 



r- » 1^ Qymnosperms, the pmes and their allies. 



2. Pteridophytes. The fern plants and their allies. 



3. Bryophytes. Moss plants and their allies. 



4. Thallophytes. The Thallophytes form two groups : the Algse 

 and the Fungi. 



The extent of the plant kingdom can only be hinted at, because 



