658 BOWMAN— ECOLOGY AND 



These leaves are put out successively with very short internodes 

 until the reserve food in the hypocotyl is exhausted and the seedling 

 dies. The same sequence of events happened in the laboratory 

 cultures described in a previous chapter in which some young seed- 

 lings were set out in boxes of sand about fourteen inches deep and 

 watered daily with sea water. The plants eventually died through 

 the exhaustion of reserve food and an inability to compensate the 

 loss in food by the activities of new synthetic tissues. The plants 

 were kept in full sunlight in coarse sand and merely watered with 

 salt water, the amount in excess of that held in suspension in the 

 soil flowing out of the box below. 



Mangrove seedlings have an equally hard time in getting a 

 foothold on rocky shores as described by Crossland.^'^ He observed 

 that the hard coral rock of the Zanzibar Reef formed a plane floor 

 with very little mud and many small cracks, but was puzzled to see 

 how the Rhizophora became planted in such small holes. While 

 Crossland does not mention the density of the water, it seems that 

 the water along these reefs must have been largely diluted with 

 fresh water since he remarks that the seedlings floated vertically. 

 By close observation, he noticed that the eddy and current gave a 

 twirling motion to the seedling, which in turn produced a boring 

 action on the shallow bottom until the radicle became lodged in a 

 little crack. Success for anchoring on these reefs depended on 

 quiet water and gentle ripples and suitable crevices on the bottom. 



In connection with the dispersal and anchorage of seedlings, a 

 number of observations were made on the character of the bottom, 

 the depths of the water, etc., on the shores of Key West, Stock Island 

 and other adjacent keys (Fig. 4, PI. VIII.). Key West being com- 

 posed of hard oolithic rock and mud flats of hard precipitated mud, 

 the conditions observed by Crossland at Zanzibar are duplicated 

 at some places and seedlings which take hold in the crevices of this 

 hard oolite cannot be pulled up, but the root will break off, owing 

 to the tenacious hold in the cleft. On these flats both Avicennia and 

 Rhisophora seedlings were observed starting growth in 8-37 centi- 

 meters of water at high tide. On Stock Island the same conditions 



155 Crossland, C, " Note on Dispersal of Mangrove Seedlings," Annals of 

 Botany, XVII., p. 267. 



