50 MY GARDEN. 



them suddenly from a moist to a dry atmosphere, as the leaves 

 cannot adapt themselves at once to the changed conditions. 



The fate of many plants depends upon the amount of water sup- 

 plied to the root. The health of an Erica cannot be maintained, 

 except by the most careful watering ; many plants are killed by 

 being kept too dry or too wet, and the skill of a gardener is nowhere 

 more shown than in his capacity for successful watering. 



Plants will not, however, live with air and water alone. They 

 must be supplied with nitrogenized compounds and mineral ingredients, 

 particularly phosphates and salts of potash. The quantity of potash 

 in the ashes of plants is large, but varying with each plant. In fir 

 it is about half a part per thousand ; in elm it is 4, in vine-shoots 

 it is 5-J-, in fern it is 6J, in bean-stalks it is 20, in wheat straw it is 

 47, and in fumitory it is 79 parts in a thousand. In wine the potash 

 is frequently deposited as cream of tartar on the sides of the bottle. 

 Curiously enough, in sea-plants or plants growing near the sea, soda 

 takes the place of potash ; and hence it is usual to salt asparagus and 

 sea-kale beds, both of which plants grow near the sea. 



Many plants contain silex, as the sugar-cane, and various grass 

 stems ; and all plants of necessity require phosphates for their growth. 

 Some chemists suppose that most earths contain an ample supply of 

 the chief mineral ingredients required for plants. This, no doubt, is 

 the case when top spit loam is used ; otherwise the soil probably be- 

 comes, at times, exhausted of its mineral constituents. It is a lament- 

 able fact that we have not yet sufficient knowledge of the exact mineral 

 constituents of the various species of plants, much less of the exact 

 quantity of salts which ought to be added to the soil. 



It is curious that, although clay is so useful for the growth of 

 most plants, there is no instance of an organic body having aluminium 

 in its composition ; but clay performs an important part in retaining 

 various substances used by plants for food. 



In the absence of more exact knowledge, the best mode of sup- 

 plying the necessary food to plants is to use the excreta of animals. 

 This contains all the changed matters of plants on which they have 



