26 THE SYNTHESIS OF CARBOHYDRATES 



before F. F, Blackman's experimental researches on vegetable 

 assimilation and respiration that the subject was really criti- 

 cally examined. Matthsei * at the outset of her work on the 

 effect of temperature on carbon assimilation found that in 

 addition to the influential external conditions there is an 

 important internal condition of a plant or plant member, the 

 result of previous treatment such as excess of food, starvation, 

 and change in temperature. 



This is a common experience ; thus Harder f found that the 

 blue-green alga Phormidium foveolarum, if cultivated in a light 

 of low intensity, can, in the photosynthetic process, make 

 use of light of lower intensities than can plants grown in high 

 light intensity. Similarly plants cultivated in strong light 

 can assimilate more readily in such light than can plants 

 which were previously cultivated in weak light. Likewise 

 for temperature J : in submerged aquatic plants cultivated 

 for three months at a low temperature, 4°-8° C, carbon 

 assimilation is less at i8° C. than at 8° C, but those cultivated 

 at a high temperature, 20° C, show a rise in carbon assimi- 

 lation with increasing temperature. In higher light inten- 

 sities, on the other hand, both cultures show a rise in carbon 

 assimilation with increasing temperature, but the rise is more 

 rapid in those plants grown at higher temperatures. Warburg 

 and Negelein § observed that when Chlorella was cultivated 

 in a high light, but a small proportion of the available energy 

 was photosynthetically employed, but when grown under 

 a low illumination the reverse obtained. Stanescue || also 

 found that lilac and other plants if kept in darkness for 48 

 hours, so that the leaves are freed from starch, show a more 

 rapid carbon assimilation than the leaves of plants grown 

 in normal conditions, although the maximum assimilation is 

 attained at about the same time of day. 



Such facts have a most important bearing on experimental 

 results, so that in order to have comparable figures it is 



* Matthwi : " Phil. Trans. Roy. Soc," B, 1904, 197, 47. 



t Harder : " Zeit. Bot.," 1923, 15, 305. 



X Harder : " jahrb. wiss. Bot.," 1924, 64, 169. 



§ Warburg and Negelein : " Zeit. phys. Chem.," 1923. I<> 6 > I9*- 



l| Stanescue : " Coinpt. rend. Soc. biol.," 1926, 95, 132. 



