24 THE BOOK OF NATURE STUDY 



good results; sunflowers do not. In Fig. n three seedlings are 

 represented : A was grown in distilled, B in water culture solution 

 minus calcium nitrate, and C in the pure water culture solution, 

 which had been carefully sterilised. The drawing was made at 

 the end of a fortnight, and certainly shows that C was thriving best. 

 The glass vessels were wrapped in brown paper, in order to protect 



ABC 



FlG. II. Seedlings of wallflower. A, in distilled water; B, in 

 water culture solution minus calcium nitrate ; C, in water 

 culture solution. 



the roots from the light. The effect of leaving out any salt, 

 necessary for the food of the plant, can be thus demonstrated. 



Experiments of this kind show that all plants require certain 

 elements if they are to thrive well ; but not all the mineral salts 

 found in the soil are essential to every plant. It is a well-known 

 fact that a chalky soil has a flora of its own, because certain 

 plants must have lime. Others again hate lime, and are not 

 found on either hard limestone or chalk. The preference of 



