8 The American Naturalist. [January, 



fossil. It has frequently happened, therefore, that when a form 

 has been described originally as a plant, this identification 

 has been accepted by subsequent worker-, and only after many 

 observations have been made and many treatises written, does 

 the original opinion change. This is well shown in the case 

 of Scolithus. Originally described as a plant, it was retained . 

 for many years in the vegetable kingdom, and only after 

 numerous investigators had examined it, was it definitely re- 

 ferred to the animal world. 



To secure an answer to the query, " what are the chances for 

 the preservation of. algse as fossils ?" It becomes necessary to 

 observe what is going on in modern oceans and the ocean 

 margins to-day. In all favorable localities seaweeds occur in 

 wonderful profusion. Some varieties live only between tide 

 marks; others only below tide and to a depth of 15 fathoms; 

 others at still greater depths, the growth of these deeper water 

 forms, however, being limited by the penetration of light, 

 vegetation ceasing entirely at depths between 100 and 200 

 fathoms. These plants occasionally form great masses in the 

 eddies caused by oceanic currents, and cover many square 

 miles of surface. This is the case with the Sargasso sea in 

 mid Atlantic: the sea of kelp off the Falkland islands, and 

 that off the coast of Japan. Some species are tough and 

 leathery, and have thick stems and long fronds, some* of these 

 reaching a length of 300 feet. Some are fine and feathery, 

 branching so as to form innumerable minute divisions. Some 

 are hardly more than masses of jelly ; and some are covered 

 with a calcareous coating and are thus more or less hard and 



known commonly as Nulliporrs. 



The structural characters of the algse as a class, are strongly 

 against their preservation under any sort of cover for any long 

 period of time. The tissue is a mass of loosely united cells, 

 often with scarcely more than sufficient coherence t«. hold to- 

 gether; and even in the tough ami leatherv varieties, the cells 

 have little consistence, are all of one character, and retain their 

 form for only a short period when buried. The late Prof. Leo 

 Lesquereux studied the possibilities of preservation of ahie, 



