188 Mineral Nutrition of Plants 



HISTORICAL OBSERVATIONS, DEFINITIONS 



Probably the earliest experimentation on this subject was by Wood- 

 ward (94) in 1699. He observed the growth of plants in various types 

 of solution, concluding that "earth, and not water, is the matter that 

 constitutes vegetables." Later, investigators recognized the limitation of 

 this conclusion and each added to the realization that "plants are made 

 of chemical elements obtained from three sources: air, water, and soil; 

 and that the plants grow and increase in size and weight by combining 

 these elements into various plant substances" (29). Advancement was 

 attained through the efforts of such men as De Saussure (22), Liebig 

 (40), Boussingault (4), and Sachs (7/). These physiologists relied as 

 usual on the progress in knowledge afforded by their contemporary 

 physico-chemists. This historical advance in knowledge is ably outlined 

 by Reed (6y) in A Short History of the Plant Sciences. 



Absorption and accumulation 



Numerous early analyses of plants showed the composition of their 

 various parts. Although not clearly recognized then, it might have been 

 inferred from such data that inorganic solutes were accumulated within 

 the plant from external sources. Probably the first clear evidence of 

 accumulation came from observations of Wodehouse (9^). Affirmation 

 of inorganic solute accumulation came rapidly through observations of 

 many workers including Cooper and Blinks (20), Brooks (6), Col- 

 lander (/6), Hoagland (28), Osterhout (5^), and their associates. All 

 these studies, for expedience, were performed with algae from marine, 

 fresh, and brackish water. A summary of some of these data is pre- 

 sented in Table I (see 28, 5^). 



Permeability 



Similar, specific experimentation on inorganic solute absorption was 

 concurrently and subsequently pursued with other plant materials. 

 Often the results were included under the title of permeability studies. 

 These earlier experiments included the course of absorption with time, 

 effects of external inorganic solute and hydrogen ion concentration, 

 temperature relations, and the like, with isolated blocks of "storage" 



