130 PLANT PHYSIOLOGY 



chloroplasts and the constitution of chlorophyll. Neither of these, 

 however, is absolutely essential to further physiological observa- 

 tions of a fruitful kind. One of the questions long ago raised is still 

 pertinent: what is the connection between chlorophyll and the 

 plastid in which it is imbedded? An answer to this question may 

 perhaps afford in time an answer to the general inquiry as to the 

 location of the true photosynthetic property. If chlorophyll is al- 

 ways the same chemically, it is perhaps probable that the first pro- 

 duct of photosynthesis may always be the same, although this is 

 not necessarily true. In any case, the chief problems hinge upon the 

 method of decomposition of carbon dioxide and water and the syn- 

 thesis of the first organic product. Neither the hypothesis of Bayer, 

 Erlenmeyer, Crato, Bach, Putz, nor any other, has, to any consid- 

 erable degree, been made capable of experimental proof, although 

 that of Bayer has been most generally accepted. Each of these 

 assumptions offers some suggestions for future work. Perhaps it 

 may as well be said that they, to a certain extent, bias future re- 

 search. Nevertheless, even when the chemical reactions in this 

 synthesis become known it may yet remain problematical how the 

 energy of sunlight, that is, of those rays most absorbed, with wave 

 lengths of 660 to 680 ^a, is made available, or whether it is this energy 

 directly or indirectly which is concerned in the decomposition. It 

 has been well assumed that the light-waves may not be immediately 

 serviceable, but only after the transformation into other forms of 

 energy. Further, it is not known to what extent this energy is oper- 

 ative in subsequent transformations. The conditions under which 

 photosynthesis occurs have been worked out with a fair degree of 

 accuracy, the status of these problems having been well set forth 

 by Ewart and others. It is known that when deleterious agents act 

 at a given concentration merely to inhibit the assimilatory function 

 (the cell not being permanently injured) there is no evident change 

 in the chlorophyll, from which it has been inferred that the assim- 

 ilatory arrest has its origin in the plasmatic stroma. In all cases 

 photosynthesis cannot long proceed except under conditions of 

 health of the protoplasts. Nevertheless, the effects of deleterious 

 agents have not always been studied by very delicate tests, and 

 further attention might be bestowed upon this matter by the use of 

 the photobacterial method, or other delicate methods, recently sug- 

 gested, for it is of considerable interest to determine the relation 

 of the photosynthetic activity to such agents as compared with 

 other activities. 



Recently the effects of temperature on photosynthesis have been 

 carefully worked out by Miss Matthaei. She states that the curve 

 of synthetic activity rises with the increased temperature, that it 

 is in general convex to the temperature abscissae and somewhat 



