6 THE NATURE AND WORK OF PLANTS 



5. A species. — In an examination of a number of 

 sugar maple or red maple trees it will be seen that 

 tliey are not all exactly the same size, shape, and 

 color, but that the red maples show some differences 

 among themselves. In the same manner the violets 

 with yellow flowers are not exactly the same shape 

 and size as to leaves and stems. Still the yellow 

 violet plants are more like each other than they are 

 like the blue violets. 



We are now ready to define a species, and can say 

 that a species is a group of individuals very much 

 alike one another, but unlike the individuals of 

 another species. Further, if the seeds of the yellow 

 violet are planted, they will germinate and form 

 plants which are like those from which the seeds 

 were taken. It may then be said that the seeds of 

 any species reproduce or give rise to the same kind 

 of specimens as those which bore the seed. The seeds 

 of blue violets always produce blue violets, those of 

 yellow violets always produce yellow violets, and so 

 on through the whole list of over a hundred thou- 

 sand species of plants which form seeds. The groups 

 of individuals which represent the species may alter 

 their habits and general appearance, little by little, 

 from generation to generation, until in the course of 



