1917 Riffg: on Bladder Kelp 317 



ever, than normal seasons of the region. The large number of cloudy and 

 rainy days undoubtedly saved many kelps from serious desiccation dur- 

 ing low tides. Muenscher^- found that the average time that Nereocystis 

 plants could withstand desiccation on the beach at Friday Harbor, Wash- 

 ington, in bright sunshine without resulting in death was 1 to 2 hours. On 

 this basis either desiccation or light intensity must certainly be an im- 

 portant factor in the death of kelps above the line of low tide. 



The observations at Lincoln Beach suggest that (c) is also a factor to 

 be carefully considered. If the kelps were being so roughly used as to 

 beat off nearly all of their fronds, death would certainly result from long 

 continuance of this treatment. The shingle on a gently-sloping beach is 

 shifted about a great deal by water movements, and it seems probable 

 that this may cause the grinding to death of many young kelps in the lit- 

 toral zone. It is possible that in the case of young plants attached 

 to small stones, water movements may result in the transportation of 

 plants and stones together to a higher position on the beach and thus in- 

 crease the danger from desiccation. 



Since the fronds of this kelp hang directly downward in quiet water, 

 but are swept out horizontally very near the surface of the water in strong 

 tidal currents, it would seem that this may be an important factor in the 

 greater abundance and better development of the plants in the latter sit- 

 uation than in the former. Light for photosynthesis would, of course, be 

 more abundant in the second case than in the first due to both the changed 

 position of the fronds with reference to the light rays and also to the 

 smaller amount of water through which the light would pass in reaching 

 the fronds. Since the main source of carbon for food synthesis in these 

 plants must be the atmosphere, the second position of the fronds must be 

 the more advantageous for obtaining this carbon, whether the plant gets 

 its carbon directly from aqueous COo or from bicarbonates. 



It is evident, of course, that a complex of factors determines the loca- 

 tion of kelp beds. These have been discussed in the papers cited near the 

 beginning of this paper and by Miss Hurd.^' Where kelp is lacking un- 

 doubtedlv in many cases some one factor has become the limiting one. al- 

 though all of the others may be present. No doubt different factors be- 

 come the limiting ones in different cases. The difficulties of removing what 

 appears in any case to be the limiting factor in the distribution of the 

 );]ant are, of course, very great. 



In the cases in which new kelps appeared at the surface of the water 

 following the cutting of portions of the beds in the Queen Charlotte Is- 



laMuenscher, W. L. C. Ability of seaweeds to withstand dessication. Puget 

 Sound Marine Sta. Pub. 1:19-23. 1915. 



i.THurd, Annie M. Factors inlluencinsr the growtli and distribution of Nere- 

 ofvsti.'=! luetkeana. Puget Sound Marine Sta. Pub. 1:185-197. 1917. 



