288 



PHYSIOLOGY, SYMBIOSIS, ETC. 



At the present time further studies are required in order to ascer- 

 tain the mechanism involved in the gradual change in value of the 

 temperature for optimum assimilation as one passes from cold to 

 warm weather and vice versa. The explanation of this phenomenon 

 should provide us with the clue to the correlation between algal 

 distribution and temperature. 



We may now turn to other aspects of algal physiology, and here 

 one may mention some results of Haas and Hill (1933) who found a 



Assim 



260r 



220- 



180- 



140- 



100 



Fig. 186. Assimilation of winter plants of Fucus serratus at varying temperatures 



and in different light intensities. = vveak diffused light, = strong 



diffused light, - • - • = sunlight. (After Lampe.) 



correlation of fat content with the vertical distribution, or in other 

 words with the duration of exposure (cf. Table VIII). 



The produc'^s of nitrogen metabolism, however, are not corre- 

 lated in the same way. The algae are also characterized by an 

 absence or paucity of free sugars, their place being taken by sugar 

 alcohols such as mannitol. As these are probably secondary pro- 

 ducts derived from the free sugar, the latter is not to be found 

 because conversion to a sugar alcohol removes it as fast as it is 

 formed. It has recently been discovered, however, that the per- 

 centage of mannitol together with another substance, laminarin, in 

 the alga Eisenia hicyclis tends to reach a maximum in the evening 



