PUTEID YEAST— WATEI^-LIME. 551 



because they are in a state of debiKty, is at present one of 

 those uncertain subjects which are greatly in need of careful 

 experimental investigation. 



Putrid yeast is one of the most powerful of the nitrogenised manures ; 

 and it consists chiefly of fungi in a state of decay. The dark green 

 colour assumed hy the grass of fairy rings seems to show how large a 

 quantity of nitrogenous matter Agarics possess. The property which 

 such manure possesses of causing an excessive production of green parts 

 is apparently exemplified by the tendency which Roses, manured with 

 rank matter, have to form such green leaves in their centre as are 

 represented at page 84. 



The only natural fluid which is of itself a food for plants is 

 water ; and there can be Httle doubt that, independently of its 

 important offices as a solvent and a vehicle of other matters, it 

 does directly contribute to Vegetable nutrition. It forms more 

 than half the weight of fresh vegetables. When introduced iuto 

 a plant it is decomposed and recomposed under the influence 

 of vital force. Its energy is increased by an augmentation of 

 temperature, to which may no doubt be ascribed, in part, the 

 powerful effect of bottom-heat. 



Of Soluble Substances those which need engage the 

 attention of the gardener are chiefly, 1, Lime ; 2, Potash ; 

 3, Soda ; 4, Phosphoric acid ; and 5, Sulphur. 



Lime. — When this substance is mixed with decayiag matter, 

 it hastens its decomposition, and renders it more easily assimi- 

 lable by plants. This is its chief horticultural value, if regarded 

 as a manure. (See p. 528.) In old cultivated land rich in 

 humus it suddenly increases productiveness in a remarkable I 

 degree, increasing the properties of dormant animal or vege- 

 table manure. Hence it has a most important effect in kitchen 

 gardens. But Umed land soon loses its productiveness unless l 

 manure is subsequently applied ; and poor soils are soon run ( 

 out by it. To some plants, such as many Conifers, it is inju- 

 rious ; to others it appears to be an indispensable article of 

 food, such as Potatoes, Saiatfoin, Barley, Beet-root, Peas, 

 Clover, &c. It also expels ammonia from manure. 



Combined with sulphuric acid it forms Gypsum (Sulphate of 



