TRANftAfiTIONS OF SKCTtOX K. i*07 



j)lants) have an advantage over plants witbont (mosses) in being able to convert 

 a higher proportion of the CO,, supplied. 



(-2) No depressing eil'ect of CO^ on assimilation could be detected up to a point 

 when the supply was about one-third saturated, corresponding in land plants to 

 an atmosphere containing 33 per cent. 00^. This supply is from thirty to fifty 

 times as rich in COo as tap-water. 



(3) Water-plants are extraordinarily sensitive to external conditions. A 

 night in the laboratory will considerably depress the assimilation, and a week 

 will reduce it to very small dimensions. In order to get results as constant as pos- 

 sible the plant was always, after this sensitiveness had been realised, gathered on 

 the morning of the experiment and in as green and fresh a condition as possible. 



Plants unhealthy to the eye, though they assimilate less than normal for the 

 particular light and temperature, yet respond to changes in the limiting factor in 

 the same way as healthy plants do. 



4. The Carbohydrates of the Snoivdi-ojy Lea/ and their bearing on the First 

 Sugar of Photosynthesis. By John Parkin, M.A. 



The main purpose of this research is an attempt to extend our knowledge 

 regarding the sugars which appear in the leaf as a direct effect of photosynthesis. 

 Few additions have been made to this subject since the publication of Brown 

 and Morris's important results in 1893.i From an examination of the sugars in 

 the leaf of Tropceolum majus these authors were led to the novel conclusion that 

 sucrose (cane sugar) is the first carbohydrate to arise in photosynthesis, rather 

 than glucose, the hitherto accepted view. This theory was criticised adversely on 

 the grounds that the sucrose might come from the maltose, which is formed from 

 the leaf-starch. 



For this investigation a plant has been selected {Galanthas nivalis, the 

 snowdrop) which never under ordinary conditions produces starch in its mesophyll ; 

 consequently the problem is not complicated by the occurrence of maltose, and 

 hence sucrose, if present, could hardly have this sugar for its source of origin. 



Sucrose has been found to occur abundantly in the snowdrop leaf, along with 

 glucose (dextrose) and fructose (levulose). About forty duplicate analyses have 

 already been made of leaves picked at different periods of the spring, at various 

 times of the day and under diverse conditions. The work, as far as it has 

 progressed, allows the following conclusions to be provisionally drawn : — 



1. The total quantity of sugars in the leaf is considerable — 20 to 30 per cent, 

 of the dry weight as a rule. 



2. The amount of sugar in a single leaf increases from above downwards, at 

 the same time the ratio of the sucrose to the hexoses (glucose and fructose) 

 diminishes. 



3. The proportion of sucrose to the hexoses decreases as the season advances, 



4. At any given period of the spring the percentage of hexose remains 

 fairly constant, no matter what hour out of the twenty-four the leaves may be 

 examined, but that of the sucrose fluctuates greatly. It increases during the day 

 and diminishes during the night. Further leaves detached and insolated contain 

 decidedly more sucrose than their controls. 



5. The glucose and fructose appear present in fairly equal proportions ; the 

 analyses however as a whole point to a slight preponderance of the latter. 



6. Leaves darkened for some days still contain a moderate quantity of sugar. 

 The percentage rapidly falls during the fir.st forty-eight hours of obscurity, and 

 then remains fairly constant. Plants so treated and then re-illuminated show a 

 large increase of sucrose in their leaves, while the amount of hexose undergoes 

 little alteration. 



The above results seem more intelligible on the view that in photosynthesis 

 the formation of sucrose precedes that of the two hexoses, rather than that the 



' ' Chem.and Physiol, of Foliage Leaves,' Joiirn. Chem. Soc, Ixiii. p. 661. 



