80 



The table shows thal the forest has a more even temperature 

 than the shore, and Ihat the variations in temperature, especially 

 in the forest near the ground, are small, This agrees with the 

 experience of other investigators. Tlie Ihermograph of 1917 gave 

 the temperature for up{)er and more exposed parts of the forest, 

 near the sea. The thermograj)h of 191 (S marked the temperature 

 in the undergrowlh in a shaded place, and probably the values 

 obtained may be regarded as characteristic of the surface of the 

 ground. It is therefore these figures that in the present connexion 

 interest us more closely. 



The summer of 1918 was cold and wet, and the low temperatures 

 near the ground in the forest are therelbre not surprising. Maxima 

 by the shore are evidently lo be associated with the heating in- 

 fluence of the direct rays of sunlight on the ground. That the 

 minima by the shore do not prove lower than in the forest is 

 verv probably due to the moderating influence of the sea, A 

 consequence of this is also that the minima do not appear until 

 between 4 and 5 in the morning. In the more open parts of the 

 forest, as the eslimations for the year 1917 show, the minimum 

 values are reached one or two hours earlier. Near the sheltered 

 ground in the förest, on the other hand, minimum values appear 

 at the same time as on the shore, or even a little låter (see the 

 avt^rages Ibr 1918). It is a general characteristic of the forest that 

 maxima do not appear until 1 — 2 hours låter in the afternoon 

 than on the shore, 



The conditions of temperature in the forest are therefore evidently 

 not specially favourable lo the balance of carbohydrales. The 

 relatively high night-temperature favours the respiralion, while the 

 relntivel}^ low day temperature lessens the assimilation. The late 

 appearance of maximum temperature 2 — 3 hours after maximum 

 light is also unfavourable. 



In other respects, however, the temperature of the forest offers 

 advanlages which indirectly favour the assimilation. The risk of 

 the overheating of the tissues and of great losses by transpiration 

 is excluded. The leaves of the shade-plants are also adapted to 

 relatively high humidity of the atmosphere and regular conditions 

 of temperature: they are large and thin, and therefore the chloro- 

 phyll is exposed to direct illumination in a much higher degree 

 than is the case with the thick leaves of the sun-plants. Thanks 

 to this and to the higher percentage of chlorophyll (see Lubimenko 



