450 Theory of the Nutrition [BOOK m. 



and of the source of the nitrogen also. He showed from the 

 plants thus artificially nourished, and with due consideration 

 of the many sources of error which beset the question, that the 

 uncombined nitrogen of the atmosphere does not contribute to 

 the nutrition of plants, but that a normal increase in the 

 nitrogenous substances in a plant takes place when the roots 

 take up nitrates as well as the necessary constituents of the ash. 

 With the exception of some doubts which still remained 

 respecting the necessity of certain constituents of the ash, 

 such as sodium, chlorine and silicic acid, the source of the 

 materials which take a part in the chemistry of the nutrition of 

 plants was known before 1860; but the knowledge obtained 

 with regard to processes in the interior of the plant, the 

 origination of organic substances in the processes of assimila- 

 tion, and the further changes which they undergo was still 

 fragmentary and uncertain, and led to no general and conclusive 

 results. 



i. CESALPINO. 



ARISTOTLE had sought to determine the nature of the 

 materials which plants take up as food, and had laid down the 

 proposition, that the food of all organisms is not simple but 

 composed of various substances. This view was correct, but 

 he united with it the erroneous notion, that the food of plants 

 is elaborated beforehand in the earth, as in a stomach, and is 

 made applicable to purposes of growth, so as to exclude the 

 necessity of any separation of excrements in the plant ; this 

 error was refuted by Jung, as we shall see, but nevertheless 

 it continued to live as late as into the i8th century, and 

 ultimately quite spoilt Du HamePs theory of nutrition. 



Cesalpino, whom we have learnt to regard as a faithful and 

 gifted disciple of Aristotle, directed his speculations to the 

 mechanical rather than to the chemical side of the question, 

 and chiefly tried to explain the movement of the nutrient sap 

 in plants. He had a larger stock of material drawn from 



