40 BULLETIN 1191, U. S. DEPARTMENT OF AGRICULTURE. 
GENERAL SUMMARY. 
_ Kelp grows only where it has good anchorage. 
The most favorable depth of water is 40 or 50 feet. 
A temperature above 25° C. destroys Macrocystis. 
Winds, currents, and waves favor growth. 
Storms often tear out many plants. 
The heaviest mats of kelp are seen late in autumn and again in 
spring. Fruit is most abundant in winter. 
Macrocystis branches by the splitting of its leaves. A frond lives 
4to 7 months. A new frond grows up when an old one perishes. 
Kelp may die and disappear suddenly when conditions are very 
unfavorable for growth. It may disappear gradually under less 
adverse conditions. 
- Black rot is the most important natural destroyer of kelp. Where 
no cutting is done, it destroys many floating fronds in warm, calm 
weather. Harvesting apparently controls the disease. 
Harvesting destroys no fish spawn. Macrocystis benefits by thor- 
ough cutting through periods of two to four weeks, at intervals of 
three or four months. 
LITERATURE CITED. 
(1) BaRrTHOLoMEwW, J. G. 
Bartholomew’s physical atlas. Vol. III, Meteorology, Pl. XXI. (1819.) 
(2) CRANDALL, W. C. j : 
The kelps of the southern California coast. U. S. Senate Document 190, 
Fertilizer resources of the United States, Appendix N., pp. 209-213. 
(1912.) 
(3) DaAvipson, GEORGE. 
The Pacific coast pilot of California, Oregon, and Washington, fourth 
edition, p. 18. (1889.) 
(4) McEwen, G. F. 
Summary and interpretation of the hydrographic observations made by 
the Scripps Institution for Biological Research of the University of 
California, 1908 to 1915. Univ. Cal. Publ. Zool. Vol. 15, No. 3, pp. 
255-356, Plates 1-38. (1916.) 
(5) McRFARLAND, FRANK M. 
The kelps of the central California coast. U. S. Senate Document 190, 
Fertilizer resources of the United States, Appendix M., pp. 194-208. 
(1912.) 
(6) OstTEeRHouT, W. J. V. 
The resistance of certain marine algae to changes in osmotic pressure 
and temperature. Univ. Cal. Publ. Botany. Vol. 2, No. 8, pp. 227-228. 
(1906. ) 
(7) SETCHELL, WILLIAM ALBERT. 
The kelps of the United States and Alaska. U. S. Senate Document 190, 
Fertilizer resources of the United States, Appendix K, pp. 130-178. 
(1912. ) 
(8) SKoTTSBERG, KARL. 
Zur Kenntniss der subantarktischen und antarktischen meeres Algen. 
Schwedische siidpolar expedition. Wissensch. ergebn. 4 lfg. 6. (1907.) 
(9) THORADE, H. 
Uber die Kalifornische Meeresstrémung, Oberfiichentemperaturen und 
Strémungen an der Westkiiste Nordamerikas. Ann. Hydro. u. marit. 
Meteor. 37, 17-34, 63-77, Figs. 1-5, pls. 5, 10, 11. (1909.) 
(10) Wetts, BERTRAM W. 
A histological study of the self-dividing laminae of certain kelps. Ohio 
Naturalist. Vol. XI, No. 2, pp. 217-227, Pls. XII-XV. (1910.) 
