624 BOWMAN— ECOLOGY AND 



More recently Guppy has observed cases of polyembryony, but 

 all of the cases which he observed seem to be of the second type, 

 in which more than one seed germinated. This naturalist counted 

 eight hundred fruits on trees of R. mangle in Fiji and found only 

 nine cases of polyembryony, eight with two radicles protruding and 

 one with three. In particular localities he found as many as two or 

 three per cent, of the fruit showing polyembryony. Perhaps this 

 indicates an hereditary factor and tendency in certain trees of a 

 region for evolution to a condition of maturing and germinating 

 all four of the ovules in a fruit. No cases of polyembryony seem 

 to be reported for other species than R. mangle. 



Embryonal Development. 



The length of time required for the complete development of the 

 embryo from the time of fertilization until the fall of the seedling 

 has been estimated by some observers and actually recorded ex- 

 actly by a few who pollinated the flowers. Even in Jacquin's time^^ 

 it was recognized that it was a long and slow process, for he re- 

 marks that the time is twelve months to the dropping of the seed- 

 lings, and that it takes three months for the hypocotyl to appear 

 at the top of the fruit. 



While an opportunity was not given to observe this for R. 

 mangle by the writer on account of the brevity of the laboratory 

 season at Tortugas, some idea was gained of the relative rate of 

 growth by marking the hypocotyl of very young seedlings with 

 bands of India ink and measuring the distance of the ring from the 

 apex of the fruit, as well as the spaces between other rings on the 

 length of hypocotyl, after a period of a few weeks, June ii to July 

 15. On the former date about 20 hypocotyls were marked in the 

 above described manner with rings one centimeter apart. At the 

 end of the time on July 15, during a return trip to Key West and 

 Stock Island, where the trees were growing, it was found that 

 twelve of the seedlings were still on the trees and had made various 

 growths, viz., 5, 3, 5, 3, 6, 5, 3, 6, 5, 4, 5, 3 centimeters, or approxi- 

 mately 4.7 centimeters, growth in the thirty-four days which had 

 elapsed. 



^•'Jacquin, N. J., " Sclectarum Stirpium Americanorum," 1763, p. 141. 



