DEIPARTMENT OF MARINE BIOLOGY. 153 



A comparison of the table of dimensions of the colonies naturally attached 

 to tiles shows that the largest colonies of Favia fragum and Pontes astre- 

 oides derived from planulse that settled in the aquarium exceed in size the 

 largest colonies from planulse that settled under natural conditions. The 

 relatively smaller size of the latter may confidently be explained by their 

 being somewhat younger. But the average difference in size between the 

 culture colonies and the natural colonies is not great. Rearing colonies ob- 

 tained in this way furnishes directly positive data on the growth-rate of the 

 species represented, and also furnishes a reliable basis for estimating the 

 approximate age of other colonies discovered in nature. 



PLANTING CORALS CE;mENTED TO TILES 



A total of 96 specimens of corals in 1910 were cemented to 24 tiles, 22 of 

 which, bearing 86 specimens, were planted on stakes off the northwest face 

 of the Fort Jefferson moat-wall; while 2, bearing 10 specimens, were placed 

 in the floating live-car moored off the northwest face of Loggerhead Key. 

 When examined in June 1911 it was found that 8 specimens had been broken 

 off the tiles and that 12 had died, 3 more dying between the time of remov- 

 ing the tiles from the stakes for measuring and photographing and that of 

 replacing them on the stakes. Seven of the dead corals were on one tile in 

 the floating live-car {4 Agaricia crassa and 3 Favia fragum). It seems very 

 doubtful from other experiments that the Agaricia will survive in water so 

 shallow, directly exposed to the rays of the sun, as this coral apparently needs 

 a more attenuated light ; but the Favia was doubtless killed by the sinking of 

 the car. The other specimens that died before June 14, 1911, were 4 Astran- 

 gia solitaria and i Agaricia crassa; the 3 that died between taking up and 

 replanting the tiles were 2 Agaricia fragilis var, and i Siderastrea radians. 

 These experiments give an idea of factors influencing the life of these corals 

 and their relative hardiness. Astrangia solitaria is usually found on the reefs 

 attached to the under side of stones, etc. It probably could not stand the 

 exposure to strong sunlight in which it was placed when planted on the upper 

 surface of the tile. Other experiments showed that placing corals accus- 

 tomed to attenuated light in strong sunlight, in very shallow water, would 

 either injure or kill them. Agaricia lives in more or less shaded places and 

 appears to be a delicate coral. Why the specimen of Siderastrea radians 

 died was not explained. 



Of the 96 corals cemented to tiles in 1910, y^^ remained for further obser- 

 vation. These y^, specimens furnish important information on the growth- 

 rate and the vicissitudes of coral life, which is often a struggling life. There 

 is, especially among the less rapidly growing corals, a constant struggle 

 against overspreading organisms, which, though they may not kill the corals, 

 at least greatly retard their growth. By using the yearling colonies a judg- 

 ment may be formed of the approximate ages of young specimens ; by seri- 

 ating the specimens it is possible to estimate the age of larger specimens. 

 The growth-rate is frequently rapid, bearing out the estimates published in 

 Year Book No. 9, pp. 136-140. To present in detail the results of this series 

 of experiments would require more space than it is desirable to take here ; 

 but 7 of the experiments are illustrated on plate 4, figs. 5, 6, and plates 5 

 and 6. (For explanation of plates see page 156.) 



The result of one experiment with Agaricia gave unexpectedly important 

 information on the influence of environment on variation. On the piers of 

 the Fort Jefferson dock a thin, unifacial, subcircular, or reniform Agaricia, 

 attached by the center of the lower surfaces, is rather abundant. This seems 



