LECTURE XVII. 



THE NUTRITIVE MATERIALS OF PLANTS. 



In my ' History of Botany ' I have shown' how, resuming the teaching of 

 Aristotle, Csesalpinus, so early as the sixteenth century and before any clear idea of 

 chemical science was possessed, attempted to obtain an insight into the mechanism 

 of the nutrition of plants ; and how in the seventeenth century van Helmont 

 undertook the first scientific botanical experiment calculated to give information as 

 to the sources of the food of plants. Malpighi, the founder of vegetable anatomy, 

 as early as 167 1 made the statement that the proper nutritive organs of the plant 

 are the green leaves, and that these take up food from the air with the co-operation 

 of light. Hales, the founder of the mechanics of the movements of the sap (1727)) 

 was much occupied with the view that a large portion of the vegetable substance 

 is obtained from the gaseous condition by condensation; and much useful know- 

 ledge of various kinds was collected later, especially by Du Hamel (1758). With 

 the foundation of modern scientific chemistry by Lavoisier, at the end of the last 

 century, the theory of the nutrition of plants also at once assumed a more definite 

 form. Ingenhouss proved (1779) that the most abundant constituent of every 

 vegetable body, carbon, originates from the carbon dioxide of the atmosphere, and 

 a short time afterwards Theodore de Saussure not only established this fact for 

 all time, but it was he also who first clearly perceived the true significance for 

 the production of vegetable substance of the mineral matters taken up from the 

 earth by the roots. From the appearance of his classical work in 1804, up to the 

 beginning of 1840 or so, when Justus von Liebig and Boussingault made renewed 

 and zealous studies of the nutrition of plants, there lies a barren period; but, 

 stimulated by these men, the study of the nutrition of plants has been pursued 

 during the last forty years with great zeal and excellent results. We may in fact 

 say that few departments of science have been cultivated more patiently and with 

 better results than this. The complete revolution which rational agriculture and 

 forestry have experienced through the establishing of the theory of the nutrition of 

 plants, proves how much has been accomplished in this department It would 

 extend far beyond the scope of this lecture to reproduce even briefly the substance of 

 the literature of the subject. The most significant result of the development of 



' Cf. my ' Geschichte der Botanik^ Munchen, 1S75. 



