MANAGEMENT OF GREENHOUSE PLANTS. 79 



pots should be sometimes loosened to a moderate depth, 

 and replenished with a portion of fresh compost. 

 Plants kept in private houses are often killed with 

 kindness. The temperature of a room in the winter 

 need not be more than ten degrees above freezing. If 

 plants are healthy, they may be kept so by attention 

 to the preceding hints ; unhealthiness generally arises 

 from their being subjected to the extremes of heat, cold, 

 or moisture, or from total neglect. 



In order that the ideas above advanced may be duly 

 considered, it may be useful to indulge in a more 

 minute description of the nature of plants, and to show 

 in what manner tne elements operate upon them. It 

 is an acknowledged fact, that the roots of plants re- 

 quire moisture, and therefore penetrate the earth in 

 search of it, and that the plants themselves are greatly 

 nourished by air, and spread their branches and leaves 

 to catch as much as possible its enlivening influence. 

 Light also is so far essential, that there can be no 

 colour without it ; witness the blanching of celery and 

 endive, where the parts deprived of light become 

 white ; place a plant in almost any situation, it wiH 

 invariably show a tendency to turn to the light ; the 

 sunflower is a striking example of this singular fact 

 As the leaves supply the plant with air, and the fibres 

 of the roots supply it with nourishment, to strip off the 

 leaves or destroy the fibres, is to deprive it of part of 

 its means of support. Having shown that air and 

 water are essential to vegetation, and light to its 

 colour, experience shows us that heat, in a greater or 

 less degree, is not less necessary to the growth of 



