86 GEORGE B. RIGG 



when germination took place in these cases is lacking. It scarcely 

 seems probable to the writer that the spores of this plant would 

 rest from midsummer until the following spring. Setchell, how- 

 ever, has actually followed "the same group of individuals through 

 their life history and the result shows that the period of active 

 existence is about nine or ten months and within the period of one 

 year." He finds that they appear in February and March and 

 disappear in December or January. In the Puget Sound region 

 the plants reach the surface of the water in early summer and dis- 

 appear by drifting loose, in late fall and early winter. This 

 certainly suggests an annual plant and in reporting on this species 

 with reference to its probable economic importance the writer 

 has regarded it as an annual, although he has himself seen no 

 evidence as to whether the spores germinate in mid-summer as 

 soon as they are discharged or whether they rest until the follow- 

 ing spring and then germinate. 



The authors cited above (I.e.) have discussed the length of this 

 plant and have full}' cited the literature of the subject. The 

 writer of this paper has never known of a specimen of the plant 

 exceeding 24 m. in length. A plant of that length was measured 

 by Zeller at the Puget Sound Marine Station in July, 1911. Frye 

 reports individuals 21 m. in length. The writer estimated the 

 length of many specimens in the vicinity of Friday Harbor, Wash- 

 ington, during the summers of 1908, 1910 and 1911 and in various 

 parts of the Puget Sound region during 1911, by pacing them 

 and has never found one exceeding 23 m. 



There are evidently three principal factors that determine the 

 habitat of the giant kelps, the depth of the water, the movements 

 of the water, and the character of the bottom. The writer has 

 frequently determined roughly the depth of the water in which 

 the large kelp beds are found in the Puget Sound waters and along 

 the American shore of the strait of Juan de Fuca by pulling up the 

 kelp including the holdfast and measuring the stipe and pneu- 

 matocyst. By this method the maximum depth of water found 

 in any of the kelp beds was 8 fathoms at high tide. Vigorous 

 plants forming dense beds are frequently found in not more than 5 

 fathoms of water. The length attained by the mature stipe seems 



