LECT. V.] THE ROOT. SOILS. 217 



tative powers weakened, and rots. This is par- 

 ticularly the case in winter ; for, as the vital energy 

 of the plant is then much lowered by cold, a dis- 

 ease of the vegetable takes place, similar to what 

 happens in a leucophlegmatic state of the animal 

 body, from which the plant rarely recovers. The 

 most efficient soil, as far as water is concerned, is 

 that which contains a due mixture of carbonate 

 of lime, sand, and pulverized clay, with some ve- 

 getable or animal matters ; and in which the ma- 

 terials are so mingled as to remain loose and per- 

 meable to the air. This soil is calculated not only 

 to retain the water in proper quantity ; but also to 

 absorb it from the atmosphere, which is one great 

 source of the supply that vegetables require : for 

 water, as has been already remarked, is requisite 

 for rendering the other matters in soils sufficiently 

 soluble to be taken up by the roots of plants. All 

 the earths are more or less soluble in water : thus 

 lime is taken up readily in its pure state ; and also 

 if the water contains much carbonic acid in solu- 

 tion, when the lime is in the form of chalk, or a 

 carbonate, in the proportion of about <r ir part of 

 its weight. Clay is soluble in a minute proportion 

 in rain water : silica even may be retained in so- 

 lution by the aid of carbonate of potash ; and in 

 the minute state of division in which it is preci- 

 pitated from an alkaline solution, it is soluble in 



