154 REPORTS ON INVESTIGATIONS AND PROJECTS. 



to be a variety of Agaricia fragilis (Dana). On the reefs off Loggerhead 

 Key an Agaricia of massive form, several inches in diameter and of some- 

 what less height, is abundant. This appears to be the same as Agaricia crassa 

 Verrill. One specimen of the thin Agaricia fragilis form attached to a tile in 

 June 1910 had by June 191 1 assumed the Agaricia crassa growth-form. This 

 specimen was attached by its entire lower surface and seems to have had its 

 growth-form influenced by the wide basal attachment. It is evident that 

 there is here one species of Agaricia that under different conditions assumes 

 different growth-forms. In very quiet water it is thin, orbicular, or reni- 

 form, with a slight basal attachment at its center, while on the reefs it is 

 more strongly attached and has a more massive growth-form. But, in the 

 quiet waters, the massive growth-form may be produced by giving the nor- 

 mally thin form a wide base of attachment, or there is a reaction to contact. 

 On the reefs, when the water is strongly agitated, there is probably a clinging 

 of the peripheral polyps to the basal support ; this causes the basal attachment 

 to cover a larger area than in the more quiet waters ; then upward growth 

 from this wide base would produce the massive form. 



The number of specimens cemented to tiles was, in June 191 1, increased 

 by 37 specimens cemented to 26 tiles, 17 of which were planted on Logger- 

 head Reef and 9 off the northwest face of the Fort Jefferson moat-wall. Be- 

 sides the measuring and photographing of the specimens, they were weighed 

 before attachment to the tiles and the tiles were weighed with the specimens 

 attached. Among these specimens were young Eusmilia knorri and young 

 Manicina gyrosa. 



RECORDS OF CORALS GROWING NATURALLY. 



The records of growth of corals growing naturally and the survey of cer- 

 tain coral areas were repeated in 1911. 



Fort Jefferson wharf. — The piers of the Fort Jefferson wharf, which have 

 been annually surveyed in order to notice any changes that may take place in 

 the corals attached to them, were again surveyed in 1911. In 1910 33 corals, 

 growing attached to the piers of the wharf, were under observation for 

 growth-rate, measurements having been made of most of them. Of these 

 specimens, 3 had been broken off in 191 1, and 8 specimens under observation 

 were not observed again because of rough water at the time of inspection. 

 Records were made of 22 of the 33 specimens in 191 1 ; 4 of these were re- 

 moved and cemented to tiles. The observations were increased by 6 new 

 records. These records include several young specimens of Eusmilia knorri 

 and Manicina gyrosa. 



Fort Jefferson moat. — The annual surveys of this moat were again re- 

 peated. An account of the low tides of June 6-8, 1910, was published in 

 Year Book No. 9, pp. 135-136. The opinion there given of the ability of 

 corals to withstand atmospheric exposure was in general substantiated. Colo- 

 nies of Eusmilia, OrbiceUa, and Mccandra clivosa were killed ; specimens of 

 Mceandra clivosa, Mccandra viridis, and Manicina gyrosa were partially killed, 

 the portions saturated with water remaining alive and subsequently growing. 

 The specimens of Favia fragum grew less rapidly than during the preceding 

 year, their growth apparently having been retarded. The specimens of the 

 three species of Porites showed no evidence of having been injured. Three 

 specimens of Siderastrea radians died. As their loss may have been caused 

 by exposure between tides, this species may be more susceptible to injury 

 through atmospheric exposure than was supposed. 



