306 ON THE CULTIVATION OF THE PINE-APPLE. 



melon plants were to be removed. ; if such baskets were to be introduced 

 into the pots in which the pine-apple plants were placed in the autumn 

 of one year, they would remain sufficiently sound till the following 

 autumn to enable the gardener to remove plants of the largest size 

 without any danger of injury to their roots. It will also be necessary 

 when fruit of the largest size is required, to place the plants, at all 

 periods of their growth, at considerable distances from each other, 

 because the leaves of the pine-apple plants act less efficiently in the 

 generation of sap, in proportion as they are made to take a perpendicular 

 direction ; and this direction they are compelled to take when they are 

 laterally much shaded ; for the leaves of this plant, like the stems of 

 potatoe plants, as I have remarked in the last communication * which I 

 had the honour to address to this Society, are subject to the conflicting 

 influence of gravitation t and of light, the one labouring to give a 

 perpendicular, the other a horizontal direction to the leaves; and 

 the comparative power of one agent increasing as that of the other 

 decreases. 



I shall conclude the present communication with an account of a very 

 simple and efficient method of destroying the different species of insects 

 that infest the pine-apple plant, which I have practised during the last 

 two years with perfect success. Pine-apple plants are not at all injured 

 by having water at the temperature of 150 of Fahrenheit's scale thrown 

 upon and into them with a syringe. The mealy bug does not appear to 

 be injured by a single washing, or immersion for a short time in water 

 of the above-mentioned temperature ; but if the application be repeated 

 three or four times on as many successive days, it wholly disappears. My 

 gardener has, I have reason to believe, used water of a higher tempera- 

 ture than 150 without any injury to the plants ; but as hot water, when 

 applied in the way above-mentioned, will operate accordingly to the 

 compound ratio of its quantity and temperature, I would recommend the 

 gardener, when he first uses it, to apply it to a worthless plant, and not 

 to use water of quite so high a temperature as 150. 



Having some red spiders upon the leaves of a fig-tree in the stove, I 

 endeavoured to ascertain the effects of hot water upon these. The first 

 application of it appeared only to render them more alert and active ; a 



* See page 300. 



t The influence of gravitation upon the forms of plants is still greater than I have inferred 

 in my paper in the Philosophical Transactions upon that subject. M. Dutrochet, having used 

 very superior machinery to that employed by me, discovered, that if a seed be made to revolve 

 upon its own axis, and its axis of rotation made to dip only a degree and a half below the hori- 

 zontal line, the roots will always take the descending, and the germs the ascending line, of 

 that axis. 



