5oo A NATURALIST IN THE PACIFIC chap. 



Summary. 



(i) The strand-district of the west coast of South America is 

 divided into four zones : — 



(a) The Convolvulus soldanella zone of Southern Chile. 



(b) The Desert or Plantless zone of Northern Chile. 

 (V) The Sesuvium zone of Peru. 



(d) The Mangrove zone of Ecuador and Colombia. 



(2) The mangroves do not extend south of Ecuador or, more 

 strictly, south of Tumbez (3 30' S.). 



(3) The absence of mangroves on the tropical coasts of Chile 

 and Peru is attributed to the Humboldt current, which has so 

 influenced the climate that it has converted the sea-border of 

 North Chile into a desert and that of Peru into a region of semi- 

 sterility. 



(4) It is considered that this has been effected through the 

 prevailing winds acquiring drying qualities on crossing the cold 

 waters of the current in tropical latitudes. 



(5) To establish this it is shown that when the Humboldt 

 current leaves the coast at Cape Blanco mangroves thrive in the 

 Gulf of Guayaquil, and that when it strikes the coast again 

 near Santa Elena Point and courses along that seaboard to 

 the equator we find the Peruvian conditions of semi-sterility 

 reproduced. 



(6) The probability that the arid climate of Peru is in our own 

 time extending northward into Ecuador is pointed out ; and from 

 the presence of old coral blocks on the Peruvian beaches it is 

 considered likely that when these corals throve the mangroves 

 extended far down the coast of Peru. 



(7) It is shown from the presence of the same species of 

 mangroves on the Pacific and Atlantic coasts of America that 

 there must have been, not long ago, a communication between 

 these two oceans across Central America ; but it is at the same 

 time observed that this could not be inferred from shore-plants with 

 buoyant seeds that, like Entada scandens, occur inland, since, 

 although they occur on both sides of the continent, their 

 distribution can be explained by the transport of their seeds by 

 rivers to the Atlantic and Pacific coasts, such as we see in 

 operation on the Panama isthmus in our own day. 



(8) Stress is laid on the great development of mangroves in 

 the Gulf of Guayaquil and in the Guayas estuary ; and it is 



