98 



PLANTS, SEEDS, AND CURRENTS 



into the sea from the tree, may proceed with the hypocotylar growth 

 whilst afloat, though probably rootlets would not be produced. This 

 growth would naturally be more marked than in the case of the 

 dried seedlings experimented on. We would expect that in ordinary 

 circumstances the floating Rhizophora seedling, if prematurely 

 detached, would add some inches to its length. 



However, it does not appear that growth is long continued in the 

 case of fruits, detached in the early stage of germination, which fall 

 into the sea. Germinating fruits, with the hypocotyl protruding 

 half an inch or less, may be at times broken off from the tree through 

 the agencies of storms and animals. Such fruits sink at once, and 

 it was ascertained by experiment in fresh-water that although the 

 germinating process was continued for the first five or six days 

 under water, the protruding portion adding about 3 mm. to its 

 length, the hypocotylar growth was arrested after a week. Fruits 

 of full size, but displaying no protrusion of the radicle, made no 

 attempt to do so whilst lying for a fortnight in fresh-water. The 

 curious appearance of a Rhizophora fruit in the early germinating 

 stage, which had been broken off and was lying in the ooze under 

 the tree, led me to plant a number of such fruits in the mangrove 

 mud with the hypocotyl in the air, thus reversing the normal position. 

 Under these unusual conditions fruits with the seedling protruding 

 between 12 and 18 mm. added from 2 to 3 mm. to the length of the 

 hypocotyl during the course of three weeks and remained in most 

 cases quite healthy. 



The Proportion of Germinating Fruits of Rhizophora 



MANGLE THAT DISPLAY MORE THAN ONE SEEDLING. In my book 



on Plant Dispersal (pp. 449, 466) I deal with the fact that whilst, as 

 a rule, only one of the four ovules in a fruit of Rhizophora becomes a 

 seed, occasionally two seeds and even three seeds are developed. 

 Out of more than 2000 germinating fruits of Rh. mangle examined 

 in Fiji, mainly in the Rewa delta, about 1 per cent, displayed more 

 than one hypocotyl. In these cases there were usually two and very 

 rarely three hypocotyls, the rate of frequency of fruits displaying 

 three seedlings not exceeding 1 per 1000. These results apply to 

 the total number of fruits observed, but there were localities in 

 which the proportion of fruits bearing more than one seedling 

 amounted to between 2 and 3 per cent. 



These observations were extended in the West Indies in the case 

 of the same species, about 1000 germinating fruits being examined, 

 500 of them in the delta of the Black River, Jamaica, and the rest 

 at St. George's, Grenada. In the locality first named just 2 per 

 cent, displayed two seedlings, no fruit with three hypocotyls being 

 noticed. But considerable variation was exhibited by different 

 trees. Thus, whilst one tree gave a proportion of less than 1 per 

 cent., another gave a value of 6 per cent. In Grenada I obtained 

 quite phenomenal results, the fruits of five trees examined yielding 

 a proportion of 7| per cent, with two hypocotyls, none with three 

 being observed. But the proportions varied greatly, the respective 

 results for the different trees being 16, 11, 7, 3, 1 per cent. The 

 rate of frequency obtained by Baron von Eggers in the tropics of the 



