





























i9i 7l OSTERHOUT— ADAPTATION 147 



fauna. One who is inclined to attribute this remarkable tolerance 

 of fluctuations in salinity to a process of gradual adaptation will 

 meet with many difficulties. 



The writer recently had an opportunity, on the island of Mount 

 Desert, Maine, to observe plants which are subjected to both fresh 

 and salt water. At the mouths of brooks, in situations between tide 



marks 



surprisingly 



the 

 the 



some places tide pools are found in the beds of brooks. 



When the tide is out these 



the 



and flows in a gentle current over it. The depth of the fresh water 

 may be as much as 7 inches, and that of the salt water 2 or 3 feet. 

 The line between the two layers is sharply marked. 6 In such places 

 one portion of a plant may be exposed for several hours a day to 

 fresh water, while the remaining portion is always in salt water. 



seemed 



plant. 



What enables these plants to survive under such unusual cir- 

 cumstances ? The current explanation is that they have gradually 

 adapted themselves to these conditions. The eel grass might be 



4 As soon as the plants are covered with salt water by the rising tide, the fresh 

 water no longer affects them, since it flows over the surface of the salt water without 

 mingling much with it. 



5 Among the species which endure 6 hours of fresh water alternating with 6 hours 

 of salt water may be mentioned the following, which were kindly identified by 

 Dr. W. G. Farlow: Gomontia sp., Enteromorpha intestinalis, Monostroma Blyti, 

 Fncus vesicidosus. Some of these species, for example E. intestinalis and M. Blyti\ 

 endure much greater exposure to fresh water. Mr. F. S. Collins has noted that Ilea 

 fulvescens (Rhodora 5: 175 and 6:20; also Green algae of N.A., p. 206), Enteromorpha 

 tnicrococca (Torr. Bull. 18:336; also Green algae of N.A., p. 204), and Pilinia minor 

 (Green algae of N.A., p. 292) stand exposure to fresh water. See also Pfeffer, 

 Pflanzen-physiologie 1:415 and Oltmaxxs, Morph. u. Biol, der Algen 2:173-183. 



( x 905. 



pools 



J f roT n one layer to the other without any sign of inconvenience. The boundary 



between the two layers is easily made visible by stirring; water-logged vegetable 



there. 



pool sinks 



