HISTORICAL AND INTRODUCTORY 3 



plants grow abundantly, the reason being that all the nitre of the soil 

 is sucked out by the plants ". Kiilbel (quoted in 292), on the other 

 hand, regarded a magma unguinosum obtainable from humus as the 

 " principle " sought for. 



In his celebrated text-book of chemistry Boerhaave (41) taught 

 that plants absorb the juices of the earth and then work them up into 

 food. The raw material, the " prime radical juice of vegetables, is 

 a compound from all the three kingdoms, viz., fossil bodies and putri- 

 fied parts of animals and vegetables ". This " we look upon as the 

 chyle of the plant ; being chiefly found in the first order of vessels, viz., 

 in the roots and the body of the plant, which answers to the stomach 

 and intestines of an animal ". 



For many years no such outstanding work as that of Glauber was 

 published, if we except Hales' Vegetable Staticks (116), the interest of 

 which is physiological rather than agricultural. Advances were, how- 

 ever, being made in agricultural practice. One of the most important 

 was the introduction of the drill and the horse hoe by Jethro Tull (284), 

 an Oxford man of a strongly practical turn of mind, who insisted on the 

 vital importance of getting the soil into a fine crumbly state for plant 

 growth. Tull was more than an inventor ; he discussed in most pictur- 

 esque language the sources of fertility in the soil. In his view it was 

 not the juices of the earth, but the very minute particles of soil loosened 

 by the action of moisture, that constituted the " proper pabulum " of 

 plants. The pressure caused by the swelling of the growing roots 

 forced these particles into the u lacteal mouths of the roots," where 

 they entered the circulatory system. All plants lived on these particles, 

 i.e., on the same kind of food ; it was incorrect to assert, as some had 

 done, that different kinds of plants fed as differently as horses and dogs, 

 each taking its appropriate food and no other. Plants will take in any- 

 thing that comes their way, good or bad. A rotation of crops is not a 

 necessity, but only a convenience. Conversely, any soil will nourish 

 any plant if the temperature and water supply are properly regulated. 

 Hoeing increased the surface of the soil or the " pasture of the plant," 

 and also enabled the soil better to absorb the nutritious vapours con- 

 densed from the air. Dung acted in the same way, but was more 

 costly and less efficient. 



So much were Tull's writings esteemed, Cobbett tells us, that they 

 were " plundered by English writers not a few and by Scotch in whole 

 bandittis ". 



The position at the end of this period cannot better be summed up 

 than in Tull's own words : " It is agreed that all the following materials 



