82 



Even al raised GO2 lension Oxalis mainlains ils advantage. With 

 a CO2 percentage in llie forest of O.ss mg. per lilre and i light, 

 Oxalis assimilates about 27 % more intensively Ihan Stellaria nemorum. 

 Wilh ^veaker light (j\,) the assimilation in the air of the forest seems 

 to be about the same for the difTerent species. 



The circumstance mentioned may perhaps help to explain the 

 extreme shyness of Oxalis in regard to the light. Of the shade- 

 planls examined Oxalis is certainly the one that can live under the 

 weakesl light. Since the greater assimilaling-power of this plant 

 chiefly makes itself felt in stronger light, there seems to lie herein 

 some evidence for the theory advanced by me that the flashes of 

 direct sunlight falling on the ground are of dorainaling imporlance 

 for the life of the under-vegetation. 



In the sun-plants the strong rise in temperature induced by the 

 conslantly active sunlight involves several disadvantages, the chief 

 of which is the greatly increased transpiration. Often the sun-planls 

 lose in the middle of the day so much water that the stomata are 

 closed, and the assimilation is thus greatly impeded or ceases alto- 

 gether (see Thoday 1910, pp. 443 ff.). 



If the temperature rises above the optimum point, which, espe- 

 cially in the case of low-growing species, may easily occur, the 

 velocily of assimilation is diminished. Another circumstance lo be 

 noted in regard to the sun-planls is the accumulalion of assimi- 

 lalion-producls, which with continuously favourable conditions of 

 assimilation may reach such a degree as to arrest the assimilating 

 process. It may therefore happen that the daily production of carbo- 

 hydrales, calculated on the basis of short assimilation-experiments, 

 turns out to be higher than is indicated by the estimalions of dry 

 weight (see Lubimenko 1908). 



In the förest the light is the factor which most sharply limits 

 the assimilation; in the case of the sun-planls it is the carbon 

 dioxide. The roselte plants and the creeping heibs, however, are 

 probiibly relatively favoured, since, coming as they do inlo imme- 

 diate conlact with the ground, they are able to utilise the carbon 

 dioxide produced by it (cp. p. 68). The nature of the soil here 

 plays a great part, and the luxuriant vegetation of soil which con- 

 tains an abundance of organic subslances (e. g. manure) is certainly 



