UNKNOWN FACTORS 35 



various plants, both fresh water and marine, grown in a culture 

 solution containing gaseous carbon dioxide. The removal of 

 carbon dioxide was followed by the method of determination 

 of the hydrogen ion concentration in the culture medium. It 

 was found that photosynthesis began immediately on exposure 

 to light; at first the removal of carbon dioxide was rapid, 

 then more slowly until a maximum was reached when the 

 rate remained constant. These authors consider that under 

 the influence of light some catalyst is developed which facili- 

 tates the photosynthetic process. Finally Briggs concludes 

 that the activity of the photochemical phase of the carbon 

 assimilation mechanism in a seedling, as compared with that 

 of more mature leaves, is in some way limited : the photo- 

 chemical phase depends for its intensity not only on the chloro- 

 phyll but also upon some other factor which increases with age 

 during the early stages of leaf development. 



There is thus strong evidence of the existence of a control- 

 ling factor essential in the earlier phases of carbon assimilation : 

 whether it be enzymatic or protoplasmic, it is impossible to say. 



THE PRODUCTS OF CARBON ASSIMILATION. Much 

 investigation is necessary before the precise significance 

 of this factor can be determined : of the products of car- 

 bon assimilation, carbohydrate and oxygen are the most 

 conspicuous ; others there are, but it is unprofitable, if not 

 impossible, to consider them on this immediate occasion 

 since accurate knowledge of their part in carbon assimilation 

 does not exist. 



It is well known that according to the law of mass action, 

 chemical action diminishes as the products of the activity 

 accumulate ; the initial rate can only be maintained provided the 

 initial proportions of the reacting substances are preserved and 

 the products of the reaction removed. In the leaf a further 

 complication arises since sugar is an osmotic substance and its 

 undue accumulation may lead to a physical disturbance in the 

 synthesizing machine such, for example, as the closure of the 

 stomates. This may be averted by the conversion of the 

 sugar into starch, a marked and well known phenomenon in 

 many plants, which temporary reserve is translocated at 

 nightfall after hydrolysis. Translocation is most apparent 



3* 



