MANAGEMENT OP GREENHOUSE PLANTS. 217 



according to circumstances. In frosty weather they should 

 be kept from the external air, and watered very sparingly. 

 When water is necessary, it should be applied in the morn- 

 ing of a mild sunny day. The plants should be kept free 

 from decayed leaves, and the earth at the top of the 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 kind- 

 ness. 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 the elements operate upon them. It is an acknow- 

 ledged fact, that the roots of plants require 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 will invari- 

 ably 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 with 

 nourishment, to strip oft* 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 vegeta- 

 tion, and light to its colour, experience shows us that hear, 

 in a greater or less degree, is not less necessary to the growth 

 of plants ; it is therefore requisite, that in taking plants into 

 our rooms, we should attend to these particulars. 



The internal structure of plants is composed of minute 

 and imperceptible pores, which serve the same important 

 purpose in the vegetable as veins in the animal system ; 



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