28 Tiie'Garden. 



not less essential to tlieir continued activity. Although many 

 plants will live at a temperature much below the freezing-point, 

 yet no plant is able to grow unless the temperature is above 

 32°, for physical reasons which require no explanation. A 

 temperature permanently much higher than a plant requires for 

 its healthy growth over-excites, enfeebles, and finally destroys it. 



2. Moisture. — Moisture is obviously essential, both because 

 water itself in its pure state furnishes two of the essential ele- 

 ments which enter into the composition of all plants, and 

 because it constitutes the medium through which the other 

 substances required are conveyed into the roots. Excessive 

 moisture, however, is destructive to most plants. It is a great 

 point in horticulture to determine the degree of moisture most 

 congenial to a given species, under given circumstances. As a 

 general rule, the plant should ie most abundantly supplied with 

 moisture when it begins to grow^ and the quantity gradually 

 diminished as it approaches maturity. However, as one effect 

 of excessive moisture is to keep the newly-formed parts of a 

 plant tender and succulent, those the leaves or roots of which 

 (as in the case of lettuce, radishes, etc.) are to be eaten un- 

 cooked, should be constantly supplied with moisture. Excess 

 of moisture will also cause strawberries and other fruits to 

 swell beyond their natural size ; but their flavor is diminished 

 in the same proportion. 



8. Food. — A plant can no more live without food than a 

 human being can. Deficiency of food dwarfs it, and prevents 

 perfect development; and it must not be forgotten that the 

 presence in the soil of the nutritive elements is of no avail so 

 long as they remain in an insolulle condition. It is only in a 

 gaseous or liquid form (allow us to repeat) that plants are ca- 

 pable of receiving their food. 



4. Air. — Plants breathe (in their way), and must therefore 

 have air. Much of their nourishment is derived either ' imme- 

 diately or remotely from it. 



5. Light. — It is by the aid of solar light alone that the leaves 

 can properly perform their grand function — the assimilation of 



