SOIL CONDITIONS AND PLANT GROWTH 



unguinosum obtainable from humus as the " principle" sought 

 for. 



The most accurate work in this period was published by 

 John Woodward, in a remarkable paper in 1.699 (321). Set- 

 ting out from the experiments of Van Helmont and of Boyle, 

 but apparently knowing nothing of the work of Glauber and 

 of Mayow, he grew spearmint in water obtained from various 

 sources with the following results among others : 



Now all these plants had abundance of water, therefore all 

 should have made equal growth had nothing more been needed. 

 The amount of growth, however, increased with the impurity 

 of the water. " Vegetables," he concludes, " are not formed 

 of water, but of a certain peculiar terrestrial matter. It has 

 been shown that there is a considerable quantity of this matter 

 contained in rain, spring, and river water, that the greatest 

 part of the fluid mass that ascends up into plants, does not 

 settle there but passes through their pores and exhales up into 

 the atmosphere : that a great part of the terrestrial matter, 

 mixed with the water, passes up into the plant along with it, 

 and that the plant is more or less augmented in proportion as 

 the water contains a greater or less quantity of that matter ; 

 from all of which we may reasonably infer, that earth, and not 

 water, is the matter that constitutes vegetables." 



He discusses the use of manures and the fertility of the 

 soil from this point of view, attributing the well-known falling 

 off in crop yield when plants are grown for successive years on 



