PRESIDENTIAL ADDRESS. 17 



land, the conditions of life are fixed and the range of species 

 limited by physical environment; thus the nature of the 

 ground, whether hard or soft, sheltered or exposed, decides 

 whether a particular spot shall support eel-grass or kelp, 

 cockles or limpets, but, within broad geographic limits, 

 temperature then decides which kind of a limpet or a cockle 

 it shall be. As Dr. F. B. Sumner wisely observes, "any 

 investigation not based on knowledge of physical data may 

 be dismissed as futile." 1 Records of such physical data 

 for this neighbourhood are scanty, and it is very desirable 

 that more information should be collected, especially as 

 this knowledge has an important economic bearing on the 

 study of the migrations, spawning and abundance of food 

 fishes. 



Environment. 

 Environment of the intertidal flora and fauna may be 

 discussed under the following headings ; (1) the nature of 

 the floor, whether of sand or mud or rock, whether bare or 

 draped with vegetation, (2) the temperature of the air and 

 the water, (3) the purity of the sea, whether quite salt or 

 mixed with fresh or muddy water, (4) the action of the 

 tides and currents. The local disposition of beach animals 

 follows naturally the plant formation, such as a mangrove 

 forest, a zosteretum or a hormosiretum. So that if a beach 

 be classified for its plant contents, it will be found arranged 

 into natural faunal areas. The intertidal, like any other 

 fauna, ultimately depends for food and shelter upon the 

 vegetation. 



ROCK FLOOR. 



Since the "roots" or rather rhizoids of seaweeds convey 

 no nourishment, but merely serve as anchors, it might be 

 thought that the nature of the ground on which they grew 

 was not a matter of importance. But actually the stones 



1 Sumner, et al. Publ. Univ. Calif. Zool., xiv. 1914, p. 5. 

 B— May 5, 1915. 



