FORMATION OF SPECIAL SUBSTANCES. 101 



though of course there are all gradations between these, and in most 

 cases it is doubtful to which of the two categories a given product 

 belongs. 



Special root secretions of some importance are the acids supposed 

 to aid the roots to take into solution otherwise insoluble substances. 

 The nature and extent of use of these is much in doubt, but in any case 

 the experiment usually relied upon to prove their presence, namely, the 

 etching of a polished marble plate, is entirely inconclusive, since the 

 phenomena of corrosion shown when roots grow upon it may be ex- 

 plained by the action of the CO 2 excreted by the root in its respiration. 



64. Prepare a synoptical essay, of not over 400 words, upon 

 lant Metabolism. 



CORRELATED TOPICS. 

 Cosmic importance of photosynthesis. 

 Composition and conditions of formation of chlorophyll. 

 Photosynthesis and artificial lights. 

 Erythrophyll and its significance. 

 Chemistry of the stages in starch formation. Cases where 



* o 



starch is not formed as the product of photosynthesis. 

 Ferments, --nature and use; fermentation, and its connection 



with the "organized' ferments; culture-methods. 

 Place and stages of proteid formation. 

 Absorption of carbon other than as atmospheric CO.,; Myco- 



rhiza. 



Fundamental significance of the carnivorous habit. 

 Optimum amount of CO., in photosynthesis. 

 Corrosion phenomena. 



Etiolation. 



LITERATURE. 



Loew, O. The Physiological Role of the Mineral Salts in the 

 Plant. Bulletin 18 of the Division of Pathology, U. S. 

 Department of Agriculture. 



Ward, H. M. The Nitrification of Soils. Science Progress, 

 3, 251. Vice-Presidential address in Nature, 56, 455. 



Fischer, A., translated by Jones. Chapters X and NI in Struc- 

 ture and Functions of Bacteria. (1900, Oxford, Clarendon 

 Press.) 



