1916 



Hurdj on Growth of Nereocystis 195 



CONCLUSIONS 



1. Nereocystis luetkeana grows longer in deep water than in shal- 

 low, indicating that growth is retarded when the surface is reached. 



2. It also grows longer when deeply submerged than when floating 

 on the surface attached to logs, or artifically attached to a raft. 



3. Tension in the stipe as the result of mechanical stretching does 

 not increase the rate of elongation. 



4. Elongation of the stipe is more rapid when Nereocystis is in the 

 dark than when it is in bright light. This accounts for the greater length 

 attained by kelps in deep water; for the more rapid elongation of sub- 

 merged kelps over those which are floating; and for the great length of 

 kelps exposed to currents or tides, which, by their tendency to hold the 

 stipe in a horizontal position, delay the time of reaching the surface and 

 the consequent retardation of growth by strong light. 



5. The short kelps growing in the rapidly flowing tide stream of 

 the Argyle lagoon may find an explanation in the bright light to which 

 they are subjected because of the shallowness of the water. 



6. Less light penetrates rough water than smooth water, but whether 

 the darkening thus produced in swift currents is sufficient to affect the 

 rate of growth of Nereocystis has not been determined. 



7. Aeration and motion of the water as a controlling factor of elon- 

 gation finds support in the great length of the kelps in the currents of 

 the San Juan Channel, but is refuted by the small size of those in the 

 Argyle tide stream. 



8. The stipe and fronds of Nereocystis are unable to live when en- 

 cased in hoods which prevent the free access of water to the plant. 



9. Young kelps are able to adapt themselves to the presence of at 

 least 55% of fresh water in their environment if the change is gradual. 



10. The stipe of Nereocystis continues to elongate at nearly normal 

 rate for at least 15 days after all the fronds are removed. 



11. The pneumatocyst can resist an external pressure of 3.3 to 5 

 kg. per square centimeter as shown by the fact that it does not collapse 

 until sunken to a depth of 33 to 50 meters. 



