194 Puget Sound Marine Sta. Pub. Vol. 1, No. 17 



were large blisters on the fronds caused by the rapid intake of water into 

 the cells. The fact that no blisters were produced on the kelps for which 

 the concentration of sea water had been very gradually reduced probably 

 shows that a change in the osmotic pressure of the cells had occurred as a 

 result of the change in the medium surrounding them. However, it is 

 just possible that the adjustment was metabolic, caused by the absence 

 of chemical nutritive materials in the water. An adaptation by means of 

 the lowering of the concentration of the cell sap, which enables plants to 

 live in water that kills those put directly into it, may be intimately con- 

 cerned in the question of the ability of salt water plants to live in fresh 

 water. 



A fact which is of interest in connection with the growth of Nereo- 

 cystis is that the stipe continues to grow for at least fifteen days after all 

 the fronds are removed. In most cases the rate of growth of kelps with 

 the fronds cut off was somewhat slower than that of the controls, but 

 sometimes elongation was just as rapid. Unfortunately these experiments 

 were started too late in the summer to determine how long the stipe can 

 continue to grow without the fronds. In only one case did removal of 

 the fronds cause cessation of growth ; and in no case was there a sign of 

 death or decay. This is contrary to the results obtained by Zeller (21), 

 who found that plants with the fronds removed soon died. Frye (12) 

 found that loss of fronds causes a rise of pressure in the air cavity. 



That the pressure of the sea water as well as light may limit the 

 depth in which Nereocystis can grow is suggested by the relatively low 

 pressure which the bulb can stand without collapsing. To determine just 

 what depth of water the pneumatocyst can stand without being crushed, a 

 kelp was weighted with a large rock and lowered beneath the water by a 

 long cord marked off into spaces of one meter each. It was drawn up 

 by means of a reel and examined for signs of collapse after each successive 

 ten meter increase in depth ; i. e., 1 kg. per sq. cm. increase in pressure. 

 One of the three kelps experimented upon had the hollow part of the stipe 

 crushed flat at a depth of 33 m. while the bulb remained unbroken. The 

 bulbs of the other two collapsed when they reached a depth of 50 m. 

 This means that the bulb is able to resist an external pressure of 3 to 5 kg. 

 per sq. cm. This inability to resist stronger pressure suggests a possible 

 reason other than darkness for the absence of Nereocystis in very deep 

 water. This would confirm the conclusion reached by Frye, Rigg, and 

 Crandall (11) that the reports of enormously long kelps are exaggerated. 



