4 THE STOCKFEEDER'S COMPANION 



II. ESSENTIALS OP PLANT GROWTH. 



The exact way in which plants obtained their 

 nourishment was up to the middle of last century quite 

 a mystery, and it will be very interesting to note the 

 chief stages in this discovery : 



Water. In the days of alchemy, when only four 

 elements were recognised viz., fire, air, earth, and 

 water Van Helmont grew a willow tree in some soil 

 in a tub, and the only thing he added was water. The 

 tree grew fairly well, but as the soil was practically 

 the same weight at the finish, he concluded that water 

 was the source of food for plants. 



Tilth in Soils. Jethro Tull found, more especially 

 with the wheat crop, that frequent horse-hoeing had a 

 great effect on the yield of straw and grain ; hence he 

 concluded that if the soil were only made fine enough, 

 the small particles would be taken up by the root- 

 hairs. 



Humus. In 1800, Thaer of Halle held that the 

 humus in the soil was probably the source from which 

 plants derived their food ; but Liebig asked how 

 it was possible for humus to be the original food of 

 plants, seeing that it was itself largely decaying 

 vegetable matter. 



Cartoon. In 1804, De Saussure pointed out that when 

 a plant was burned in air, most of it disappeared, there- 

 fore he considered that the greater part of a plant must 

 be derived from the air and water. This proved later 

 on to be the case, for a Swiss scientist (Chas. Bonner) 

 noticed that when certain green leaves were immersed 

 in water, bubbles of gas sometimes appeared on the 

 leaves. Priestley found that these bubbles were oxygen 

 gas, and Ingenhaus that they only made their appear- 



