136 REPORTS ON INVESTIGATIONS AND PROJECTS. 



colonies for several hours without the usual dashing of water over them 

 through agitation by wind or ocean-swell. Two photographic illustrations 

 of the appearance of one of the reefs off Loggerhead Key are here presented 

 (plate I, figs. A and B). The corals in the Fort Jefferson moat were also 

 examined to ascertain the effect of the exposure. 



The ability to withstand exposure between tides seems to be a function of 

 the porosity of the skeleton. On the reefs the tops of the heads of Orbicella 

 annularis were bleached, and at least the superficial soft tissues were killed. 

 In the moat the superficial soft tissues of Busmilia, Orbicella annularis, 

 Mcuandra areolata, M. clivosa, and Manicina {"Colpophyllia") gyrosa were 

 killed, and the same was also the case with some specimens of Favia fragum, 

 or all corals with imperforate hard tissues. The amount of regeneration that 

 may take place from living tissue deeply situated in the skeletons can not be 

 ascertained before inspection during the next field season. It should be 

 stated that even these corals may stand atmospheric exposure if kept satu- 

 rated with sea-water. Siderastrea radians, the skeleton of which is slightly 

 perforate and is made more spongy by synapticula, withstands exposure 

 better than corals with imperforate skeletons; while the various species of 

 Porites seemed to be not at all affected by an exposure of several hours, 

 their extremely porous skeletons insuring a continuous supply of water 

 through capillarity. 



That Orbicella annularis heads are often partially killed by exposure is 

 attested by the dead summits of large heads, which are usually submerged, 

 off the western side of Garden Key. 



RATE OF GROWTH OE CORAI^S. 



The report for 1909''^ contains notes on measurements instituted to ascer- 

 tain the growth rate of corals, and a few comparative measurements made 

 in 1908 and 1909 are given. In 1910 the colonies measured in 1908 and 1909 

 were remeasured, except in those instances in which the colony had been 

 broken from its attachment or had died, and the series of measurements was 

 greatly increased. It was stated in the 1909 report that the measurements 

 were then not sufficiently accurate. An attempt has been made to remedy 

 this defect by referring the colonies to horizontal and vertical coordinates. 

 Plumb-lines were attached to the instruments to get vertical lines, and the 

 horizontal was determined by an arm perpendicular to the one to which the 

 plumb-line was attached. Nevertheless, as corals are very irregularly shaped 

 objects and grow in various positions, and as it is difficult to measure under 

 water in the ocean, even in quiet weather, only approximate accuracy can be 

 expected. Cementing specimens to tiles and photographing them before plant- 

 ing has been initiated, hoping thus to obtain more accurate results than by 

 measurement alone. It is very desirable to determine both the weight and 

 the volume of the skeleton produced in a known period of time. It will be 

 possible to determine these directly in specimens reared from larvse ; and 

 they can be closely estimated when such growth observations as are now 

 being made become sufficiently numerous. 



In the succeeding notes on the present status of the investigation each 

 species is considered separately. In several instances tentative estimates of 

 the age of average-sized adult colonies are given ; these estimates, although 

 they seem reliable, must not be considered as facts, and are being checked by 

 numbers of observations. Madreporarian colonies are limited in growth, a 

 fact which brings up for consideration the cause of this limitation. The 



* Carnegie Institution of Washington, Year Book No. 8, 1909, pp. 141-142. 



