PHYSIOLOGY 289 



whilst the mean content for day and night is not appreciably 

 different. In this alga, therefore, these substances are probably not 

 direct products of photosynthesis. It has been shown that when 

 Eisenia is kept in the dark both these substances decrease and so it 

 is suggested that they should more properly be regarded as food 

 reserve materials. 



Studies on the induction of polarity in Fucus eggs have shown 

 that unilateral light is normally the strongest determinant but that 

 polarity can also be induced by an electric current or^H gradients. 

 There is also the effect of neighbouring groups of eggs or the 

 nearest large tgg, the first rhizoid developing on the side nearest to 



Table VIII 



Ether-extracted 



fat True fat 



Pelvetia canaliculata f. libera (salt marsh) 8-62 8-o 



Pelvetia canaliculata (spray zone) 4-88 4*9 



Fucus vesiculosus ecad volubilis (salt marsh) 3-76 



Ascophyllum nodosum (middle littoral) 2-87 



Fucus vesiculosus ~\ 2-60 2*6 



Halidrys siliquosa J- (low littoral) ' 2* 18 



Himanthalia loreaj 

 Desmarestia aculeata 



Laminaria digitata 

 Pelagophycus 

 Macrocystis 

 Nereocystis 

 Laminaria Andersonii ^ 



I-2I 



0-65 



0-46 0-3 



(sublittoral) 



0-27 



0-34-0-40 



I -06 



0-65 



them. This is probably a growth substance effect since the 

 presence of growth substances has been demonstrated in eggs, 

 sperm and fruiting tips oi Fucus. In the case of polarity induced by 

 the proximity of eggs the growth substances from the neighbouring 

 ova are not necessary for rhizoid formation but are purely directive. 



General 



An investigation has been carried out by Biebl (1938) using 

 hypo- and hypertonic solutions of sea water for determining the 

 drought resistance and the osmotic relations of algae from different 

 depths. The algae studied could be placed in three groups according 

 to their behaviour but irrespective of their geographical locality. 



A. Deep growing algae which are never exposed to the air: they 

 are resistant up to a concentration of 1-4 times sea water. 



B. Algae of low water mark and the lower littoral tide-pools 



CSA - ^9 



