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SCIENCE 



[Vol. LVI, No. 1455 



■without indicating definitely, as least in the 

 case of the eurythermal species, just what tem- 

 perature limits are vitally eoneei-ned with the 

 persistence of the species. An attempt has 

 been made to establish definite temperature 

 zones, to each of which certain species are nor- 

 mal, and to explain the presence of any species, 

 normal to one zone, in a zone of different tem- 

 perature, by the fact that the invaded zone, as it 

 was designated, has its temperature raised or 

 lowered to that of the normal zone of the species 

 by some agency or condition, local or general, 

 and for a sufficient length of time to allow of 

 the reproductive processes of the invading spe- 

 cies to be effectively carried on. This idea has 

 been set forth in an article entitled "Steno- 

 thermy and Zone Invasion." {Amer. Nat., Vol. 

 54, pp. 385-397, 1920.) 



In connection with this investigation, it 

 seemed very desirable to attempt to determine 

 the behavior of a group of aquatic plants 

 other than the Alga and I turned my attention 

 to the marine spermatophytes, popularly 

 known as sea gi-asses, eel grasses, or grass 

 wrack. The inquiry, at first, was purely sta- 

 tistical, merely assembling what was known of 

 these plants as to their distribution, their 

 times of flowering, and the relation of their 

 distribution and flowering to isothei-mal lines 

 of temperature, especially to those of the max- 

 ima. The results of this inquiry are set forth 

 in a paper entitled "Gteographical Distribution 

 of the Marine Spermatophytes" {Bull. Torrey 

 Bot. Club, Vol. 47, pp. 563-579, 19^0). It 

 seems, from the data available, that out of 34 

 known species, 26 are stenothermal, i. e., con- 

 fined to a single zone of temperature of 5° C. 

 amplitude of the maxima; 6 are somewhat 

 eurythermal, occurring in two such zones; and 

 2 are broadly eurythermal, occupying 3 or 

 more of such zones. Of the last category, 

 Zostera marina L., the common eel-grass of 

 the north Atlantic coasts, is the most pro- 

 nounced and the most puzzling. After assem- 

 bling such data as were readily available as to 

 season of reproduction in different portions of 

 its range, I ventured to suggest that the normal 

 zone of Zostera marina L. must be the North 

 Temperate, whose waters possess a summer 

 temperature of 15° to 20° C, and that the 



extension of the distribution of this species as 

 far north as the Upper Boreal is due to the 

 effect of insolation upon the shallow, enclosed 

 waters of its habitat in the invaded zones, and, 

 on the other hand, that the invasion southward 

 into the northern portion of the Tropical Zone 

 is possible on account of the seasonal loweriug 

 of the temperature of the waters during the 

 winter and spring. 



Since I am able to visit the Atlantic Coast 

 only at very infrequent intervals, I appealed 

 to correspondents and to the U. S. Commis- 

 sioner of Fisheries to assist in determining the 

 exact status of the temperature conditions of 

 the life-history of Zostera marina L. The Com- 

 missioner promptly and favorably responded 

 and issued instructions to make the collections 

 desired at the stations at Key West, Florida, 

 Beaufort, N. C, and Woods Hole, Mass. At 

 the Key West station, Ezra Stiles, Jr., early 

 demonstrated that Zostera marina L. is absent 

 but that the Turtle Grass, Thalassia testudi- 

 num, is abundant and presents certain prob- 

 lems. With the transfer of Mr. Stiles to an 

 inland station these observations came to an 

 end. At the Beaufort statioai, Charles Hatsel, 

 and at two very different localities at Woods 

 Hole, K. A. Goffin have made collections 

 monthly or bi-monthly for some seventeen or 

 eighteen months, together with the proper tem- 

 perature data. I am deeply indebted to these 

 members of the staff of the Bureau of Fisheries 

 for their most valuable and painstaking co- 

 operation. 



I, myself, was able to supplement the ob- 

 servations at the stations of the Bureau of 

 Fisheries by collections made at various sta- 

 tions about Narragansett Bay, R. I., in May, 

 June and July of 1921, and Professor Thurlow 

 C. Nelson of the New Jersey Agricultural Ex- 

 periment Station kindly made collections 

 throughout the year at stations of the Oyster 

 Commission on the coast of New Jersey. 



Since Zostera marina L. grows in extensive 

 patches, whose individual plants are fairly uni- 

 form in behavior, all that is necessary is t© 

 gather a fair sized bunch of plants, dry and 

 forward with the proper data. The extensive 

 mass of material accumulated has not been 

 critically gone over as yet, but sufficient exam- 



