1 14 PLANT PHYSIOLOGY 



is, 0-.5-1 gm 2 h. As to the amounts of the various substances concerned, 

 the student will of course work these out exactly by use of the photosynthetic 

 equation, replacing molecular weights by gram weights. He will then see 

 that conventional constants may be accepted as follows: to form one gram 

 of photosynthate requires 1.5 grams, or 750 cc, of carbon dioxide, which is 

 the quantity contained in 2500 liters of air. In other words a square meter 

 of leaf in making one gram of photosynthate uses all the carbon dioxide 

 of a column of air over it 2.5 meters in height. 



As to the energy stored, this will be the exact reciprocal of that released 

 in respiration, as considered under that process later. As to the amount 

 utilized of the energy of sunlight falling upon the leaf, Brown (Nature, 

 71, 1905, 522) has shown that this is less than 1%; the fate of the remainder 

 will be noted later under Transpiration Quantities. 



Literature of Photosynthesis. This is summarized down to 

 1900 by Pfeffer, and there is a later synopsis by Josx. Some special 

 papers of particular value to students in this course, in addition to 

 those already mentioned in the preceding pages, are those by Brown 

 in Nature, 60, 1899, 474, by Timiriazeff in Proceedings of the Royal 

 Society, 1903, 421 (good summary in Botanisches Centralblatt, 96, 

 1904, 529), by Brown and Escombe in Proceedings of the Royal Soci- 

 ety, 76, 1905, 29, and by Blackman and Matthaei in the same jour- 

 nal, 76, 1905, 402, and by Brown in Nature, 71, 1905, 522. There 

 is also a very recent summary of our knowledge of the subject by 

 Czapek in Progressus Rei Botanicae, I, 1907, 468. 



2. CHEMOSYNTHESIS. 



In his study of carbon fixation through photosynthesis, the 

 student must be impressed by the importance of the kinetic 

 energy of light in the process, whence the question is natural, 

 can the process take place if the energy is supplied in some other 

 manner, and is any other manner known? In fact a case 

 is known in certain Bacteria which utilize chemical energy 

 derived from oxidation of mineral substances, a true process of 

 Chemosynthesis. The subject is one of extreme experimental 

 difficulty, and the student must seek information upon it through 

 the literature, in which there is a very satisfactory treatment by 

 Pfeffer, i, 361. Furthermore it is altogether probable that 

 much, if not most of the energy used in synthesis of proteids, 

 next to be considered, is chemical, so that proteid synthesis is 

 no doubt largely Chemosynthesis. Theoretically both Ther- 



