PHOTOSYNTHESIS 113 



thesis outside the living protoplasm, — on which the student should 

 seek information from the proper sources. He should also under- 

 stand the photosynthetic graphs of Engelmann, of Reinke, 

 and of Kohl, their meaning and the mode of their construction. 

 Photosynthesis, with its needs for exposure of much green 

 surface to light, for free access of carbon dioxide, for a supply 

 of water, for translocation of its products from the place of for- 

 mation, becomes the center of very important ecological fea- 

 tures which the student should make sure that he clearly under- 

 stands. He should embody his knowledge in a brief exposition, 

 with illustrative diagrams, making plain (a) the structures 

 which are adapted to the demands of the actual physico-chem- 

 ical process; (b) the compromises of these structures with those 

 adapted to other necessary processes of the plant; (c) the fea- 

 tures, protective or adjustive, which relate these to average or 

 ordinary external conditions; and (d) the modifications result- 

 ing from adaptation to special habits. 



Terminology and Conceptions of Photosynthesis. The student 

 will have noticed early in his study of the literature of this subject that most 

 European books name the process "assimilation" or "photosynthetic assimi- 

 lation," while American works call it "photosynthesis." The former is an 

 old term coming down from the time when the process was supposed to be 

 a part, and the principal part, of that which in plants corresponds to assimi- 

 lation in animals. We now know that the process is an entirely distinct one, 

 found only in green plants, with nothing like it in any way in animals, while 

 plants do also have a process of assimilation physiologically equivalent to 

 assimilation in animals. Hence it is better from every point of view to 

 restrict the older term to its proper function, and apply to this process the 

 very appropriate and distinctive term photosynthesis, invented by C. R. 

 Barnes in 1893 in the form photosyntax, and changed later to the present 

 form. The process is also sometimes called popularly "food manufacture." 

 (History of the word by Barnes in Botanisches Centralblatt, 76, 1898, 257.) 



Photosynthetic Quantities. As to the amounts of photosynthate 

 made, Sachs found that herbaceous plants out-of-doors in summer under 

 most favorable conditions made 1.882 grams of photosynthate per square 

 meter per hour, though Brown and Blackman have found much smaller 

 quantities. Taking all the data together, we may accept for plants under 

 best conditions out-of-doors 2 grams as an extreme, with 1 gram as a mean, 

 giving a conventional constant (page 22) of 0-1-2 gm 2 h. Studies by my own 

 Students have shown that greenhouse plants under the best of conditions 

 in winter approximate to one-half the quantities of those out-of-doors, that 



