.SI 



1908, WiLLSTÄTTER 311(1 Stoll 1<)18, j). 118), Ihe shade-ieaves are 

 able lo absorb and ulilise Ihe greatesl possihle proportion of Ihe 

 lighl available. 



The relalively low and conslanl ground-lempcraliire in the förest 

 shoiild also help to bring il aboul that Ibc siinbeams wliicli |)ei)e- 

 trale in patches do not succeed in causing too greal healing, wilh 

 consequent lessening of the relative dampness of the air. The sirong 

 light of Ihe sun-illuminated patches is utiiised in the assimilation, 

 since Ihe stomata are not closed, as I have ascertained by infiltration 

 experiments. 



In the case of Oxalis the stomata are opened even in the direct 

 sunlight, and return to their half-closed condilion in the difluse 

 light. On a sunny patch under ålders and ferns a light-intensity 

 of ^i^ was measured (Ocl. 4), and in anolher ])lace Ihe intensity 

 was ^ — ^. The stomata, except in older leaves, were complelely 

 open. In shady patches they were half- or Ihree parts closed. In 

 a bed of Oxalis at the foot of a powerful ålder the leaves on the 

 sunny side showed immediate infiltration wilh xylol. On the shady 

 side the infiltration proceeded much more slowly, or did not lake 

 place at all. 



The opening and closing of Oxalis stomata takes a time of I — 1 

 hour, and they therefore remain open for a while afler the sunny 

 patch bas passed by. Only in very sirong and conlinuous sun- 

 illumination, in more open places in the forest, does Ihe opposite 

 reaction apply, when the stomata close again. This is probably 

 due to the losses by transpiration, since Ihe leaves häng down and 

 in other respects show signs of relaxing. — In Viola paliisiris also 

 I have observed fully open stomata in the sun-illuminaled patches. 

 Here however the stomata were fully open even in the shade. 



Fully open stomata of course ha e a higlily favourable effect 

 upon the supply of CO2 lo the assimilaling cells, and from the 

 observations given the conclusion may be drawn that the shade- 

 plants fully ulilise the opporlunilies for increased assimilation olTered 

 by the combination of direct sunlight and high CO2 concenlralion. 

 The tempoiarily increased temperaluie of Ihe leaf is also a not 

 unimportant faclor here. 



From the curves in fig. 2 and from the table on p 5() it will be 

 seen that the assimilating-power of Oxalis is about 50 % grealer Ihan 

 in the other shade-planls wilh normal COj pressure and sirong 

 light, i. e. when Ihe carbon dioxide acts as the limiting faclor. 



6. — Svensk Botanisk Tidskrift 1921. 



