NO. I SMITHSONIAN EXPLORATIONS, I919 4I 



In the vegetation there are represented four of the Hfe zones 

 recognized by biologists. The Transition Zone is indicated on the 

 west slope by small areas of yellow pine timber, and east of the Park 

 are the prairies of the Blackfoot Indian Reservation, which extend 

 also within the Park boundaries along the stream valleys. The plants 

 here are chiefly herbs, with a few shrubs, and they belong mostly to 

 species which have a wide distribution over the Great Plains. By 

 far the largest portion of the Park is covered with the characteristic 

 vegetation of the Canadian Zone, which is the heavily forested area. 

 Above the Canadian Zone, around timber line (6,000 to 7,500 feet), 

 lies a narrow belt belonging to the Hudsonian Zone. The trees here 

 are mostly low and stunted, and their branches frequently lie pros- 

 trate upon the ground. Above this belt, and occupying the highest, 

 exposed slopes, lies the Arctic-Alpine Zone, whose vegetation is 

 composed chiefly of small herbaceous plants, with a few dwarfed 

 shrubs, mostly willows. ]\Iany of the species of this zone are 

 widely distributed in alpine or arctic regions of North America, and 

 some of them occur also in similar situations in Europe and Asia. 



EXPLORATIONS AND CERION STUDIES ON THE FLORIDA KEYS 

 Dr. Paul Bartsch, curator of marine invertebrates, U. S. National 

 Museum, joined Dr. Alfred G. Mayer, the Director of the Tortugas 

 Marine Biological Laboratory, of the Carnegie Institution, in New 

 York on December 28, when they sailed south for Key West to 

 make an examination of the Cerion colonies discussed in previous 

 Smithsonian exploration, pamphlets. The breeding" experiments 

 presented an entirely new phase, in the crossing, on one of the keys, 

 of the native species, Cerion incanum (Binney) with one of the 

 introduced Bahama species, Cerion viaregis Bartsch. It was this 

 discovery that made it desirable to start an entirely new set of experi- 

 ments. Furthermore, the anatomical difterences discovered in the 

 dissections of Cerions also made it desirable to gain material from all 

 the colonies now existing on the Florida Keys, in order that these 

 might be subjected to anatomization, to determine if Cerion incanum 

 is really one species, or a complex, shell characters alone being 

 insufficient to determine this point. It was for this double reason 

 that a return was made to Florida on May 2. and an exploration of 

 the keys adjacent to Miami at once undertaken. 



On the 3d Capt. Tracy and Dr. Bartsch started in the " Darwin," 

 a shallow draught launch of the Carnegie Institution, for an explora- 

 tion of the shores of the mainland of the lower peninsula and the 



