1916 Hurd; on Growth of Nereocystis 189 



Iheir natural position. The holdfasts were bound to rocks by muslin 

 strips and cord, and the rocks lowered by strings from the raft. Table 2 

 is a comparison of the rates of growth induced by the two environments, 

 and indicates that darkness is a large factor in the elongation of the stipe 

 of Nereocystis. 



Table 2. Comparison of the elongation in 10 days of plants deeply sub- 

 merged with those near the surface. 



Plant 1.9 m. in length with bulb submerged 4.6 m. elongates 7.5 cm. 

 Plant 1.7 m. in length with bulb submerged 5 cm. elongates 3 cm. 



Plant 3.42 m. in length with bulb submerged 4.6 m. elongates 13 cm. 

 Plant 3.84 m. in length with bulb submerged 5 cm. elongates 5 cm. 



Plant 3.93 m. in length with bulb submerged 4.6 m. elongates 19 cm. 

 Plant 3.73 m. in length with bulb submerged 5 cm. elongates 13 cm. 



The failure of all attempts to secure growth in darkness by means 

 of hoods of black cloth should be noted here. Strips of black lining 24 

 cm. wide and as long as the stipe to be covered, were sewed up one side 

 so as to enclose the plant in a tube the ends of which were drawn up by 

 gathering strings and tied. In every case the stipes and fronds covered 

 soon ceased growing, and decayed rapidly, some plants being quite soft 

 at the end of eight days. In one case in which the stipe grew only 1 cm. 

 in 16 days and was still alive at the end of that time, the covering was 

 removed with the result that at the end of the next 6 days it had grown 

 2.5 cm. Occasionally no elongation takes place after the hood is put on, 

 and the plant soon becomes soft. The cause of death is probably inter- 

 ference with the gas exchange. It would be interesting to try darkening 

 by means of hoods held open at both ends by wire rings, since this arrange- 

 ment would allow free access of water to the plant. 



Observations on the size of Nereocystis plants growing in different 

 environments in the vicinity of the Marine Station confirm the supposi- 

 tion that it cannot be differences in mechanical stretching which cause the 

 variations in the length of the stipe, and that it may be differences in light 

 intensity. From the unusual length of the stipes growing in the swift 

 current in San Juan Channel — some of them 18 meters long — it might 

 appear that the stretching to which they are subjected is a cause of their 

 rapid growth. But not far distant are other kelps growing in water flow- 

 ing just as swiftly which rarely exceed 60 cm. in length. They are in the 

 shallow tide stream which fills and empties the Argyle lagoon. The bot- 

 tom is gravel for the most part with an occasional rock large enough to 

 anchor a kelp. These plants are often curiously misshapen. Many have 

 fronds 60 cm. long and bulbs of normal size but very short stipes. One 

 was found with a bulb 6 cm. in diameter and a total length from holdfast 



