Factors Influencing the Growth and Distribution o*"'^ 

 Nereocystis Luetkeana 



Annie May Hurd, 

 University of Washington, Seattle. 



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It is obvious to even the casual observer that the length of the stipe 

 of Nereocystis luetkeana is largely determined by the depth of the water 

 in which it grows. Kelps growing in deep water may reach a length of 

 18 meters, while plants nearer shore are shorter, those attached near the 

 low tide line rarely exceeding three or four meters. Rigg (24) notes 

 that Nereocystis reaches its best development in water 8-10 fathoms deep. 

 Experiments were carried on at the Puget Sound Marine Station in the 

 summer of 1916 to determine whether darkness or the mechanical stretch- 

 ing of the stipe by the upward pull of the bulb causes the more rapid 

 growth of a deeply submerged kelp. Either explanation would account for 

 the facts ; because when the kelp reaches the surface of the water the pull 

 of the bulb on the stipe is lessened, hence the rate of growth if affected 

 by tension might decrease; or if the chief factor were light intensity, the 

 bright light at the surface might retard elongation. 



It is commonly known and has been experimentally proved in many 

 cases that darkness stimulates and bright light retards growth. The ex- 

 perimental work cited by Pfeffer (23) and Jost (15) is evidence of the 

 retarding action of light on the growth of leaves, stems and roots of the 

 flowering plants. According to Jost, there is a maximum light intensity 

 "affecting the generality of plants which, when exceeded, first retards 

 growth, and finally causes death. The position of the maximum is very 

 varied. It lies very low in shade-loving plants such as we find abundant- 

 ly in woods, or more especially in the sea." 



Similar results have come from work on thallophytes. According to 

 Vines (29) Brefeld found that the hypha bearing the sporangium of 

 Pilobolus microsporus grows to be eight or ten inches long if grown in 

 darkness, while usually it does not exceed one-half inch ; and that the stipe 

 of Coprinus siercocarius, usually about an inch long, may become two 

 feet long in the dark. Klein (16) (Rev, Bot. Centralb.) concludes that 

 light is the chief factor in the production of conidia in Botrytis cinerea 

 from the fact that the spores are produced so much more abundantly at 

 night or when darkened in the daytime. He reports similar results from 



(185) 



