CHAPTER I. 



HISTORICAL AND INTRODUCTORY. 



In all ages the growth of plants has interested thoughtful men. The 

 mystery of the change of an apparently lifeless seed to a vigorous 

 growing plant never loses its freshness, and constitutes, indeed, no small 

 part of the charm of gardening. The economic problems are of vital 

 importance, and become more and more urgent as time goes on and 

 populations increase and their needs become more complex. 



There was an extensive literature on agriculture in Roman times 

 which maintained a pre-eminent position until comparatively recently. 

 In this we find collected many of the facts which it has subsequently 

 been the business of agricultural chemists to classify and explain. 

 We find also both here and in the much smaller literature of mediaeval 

 times, certain ingenious speculations that have been justified by later 

 work. Such for instance is Palissy's remarkable statement in 1 563 (224) * : 

 ' ' You will admit that when you bring dung into the field it is to return 

 to the soil something that has been taken away. . . . When a plant is 

 burned it is reduced to a salty ash called alcaly by apothecaries and 

 philosophers. . . . Every sort of plant without exception contains 

 some kind of salt. Have you not seen certain labourers when sowing 

 a field with wheat for the second year in succession, burn the unused 

 wheat straw which had been taken from the field ? In the ashes will 

 be found the salt that the straw took out of the soil ; if this is put back 

 the soil is improved. Being burnt on the ground it serves as manure 

 because it returns to the soil those substances that had been taken 

 away." But for every speculation that has been confirmed will be 

 found many that have not, and the beginnings of agricultural chemistry 

 must be sought later when men had learnt the necessity for carrying 

 on experiments. 



The Search for the " Principle " of Vegetation, 1630-1750. 



The earlier investigators sought for a " principle " of vegetation 

 to account for the phenomena of soil fertility and plant growth. Van 



' The numbers in brackets refer to the Bibliography at the end of the book. 



