/f 



tne specie^- led excet> Vucua serratus ;viz. .Agcojohyllum nodosum. 

 Fucus vesciculosus, J<\ soirniis, n/.d Pexvetia comiii cul r it.p , their 

 sensibility to light differs and the oxygen factor or internal caue~ 



es t&tjS&Bfe?/ produce frequent exceptions in all but Pelvetia. 

 The rhizoids of the latter species are alwa/y sf oraed on the darker 



side of the spore, and this is the one species in which tne egg 

 is surrounded by an oogonial wall which might prevent any of he 



effects of varying oxygen concentrntion^which can net more potent- 

 ly thsn light on the spores of the other species. Rosenvinge quotes 



Kny as finding that neither light, gravity, ijor contract c?t( influ- 

 ence the point of origin of the pollen tube from pollen grains, 



but that in tne neighborhood of other grains tne tubelwill be sent 

 out from t,-.'.e side away from them, on which side the supply of 



oitygen or nutritive elements would be greater. 



-iS^SHSV, farmer and Will iaias ( iS'fv ) state/ that if Fucus spores 



/ 



are illuminated on all sides they tend to remain spherical in%tead 

 of producing B rhizoid bu t<:e elongation of one of the two cells. 

 Again(l898) they experimented with one-sided illumination with the 

 usual result that most of .he rhizoids originated on trie shaded side 

 of the spore and the others *fere turned that Iway. The fact that some 

 graw out at an angle to tne incident light 4s attributed to "the 

 character of the egg itself". 



inkler(#//1900) found the some orienting effect of light on 

 tne spores of Cy s t o s e i r a __b ar b a ta but failed to find any dffect of 



a difference in the oxygen content of the -vater. He too 



A 



that gravity and contact are not factors in the establishment of 

 polarity of the sporelings. r.e found that the direction is determin- 

 ed before the firs', division takes place. Since t is polarity is 

 established during the firstjfour hours of illumination and connot 

 changed afterwards by any change in the direction of the incident 

 light, he concludes that light can orient the spore only during 

 fertilization. 



