C>70 



JOURNAL OF THE ROYAL HORTICULTURAL SOCIETi'. 



Mangrove Seedlings, Note on the Dispersal of. By Cyril 

 Oosslancl (Ann. Bot. vol. xvii. No. lxv. p. 267 ; January 1903. With 

 figure in text). — This is an interesting record of one of the remarkable 

 ways in which planting is sometimes done by nature. In this case we 

 have the planting of a developed embryo minus the cotyledons, which 

 remain behind in the fruit. The seed of Mangrove (Rhizophora) germi- 

 nates in the fruit, the hypocotyl protrudes, attains a length of about a 

 foot or eighteen inches towards earth, and finally, by its weight, causes 

 the embryo to fall like a shaft straight into water or mud. If in mud, the 

 embryo is thus planted upright and is ready to grow. This is the well- 

 known method of planting, but there is another newly observed and the 

 subject of this note. It depends upon ripples of water and falling tide. 

 " The coasts of the whole of British and German East Africa are composed 

 of hard coral limestone of peculiar properties. . . . The erosion of the waves 

 has cut down this rock so that at low tide there is an almost plane surface 

 of rock, sloping gradually from the base of the cliffs to low- water level. In 

 creeks and sheltered places generally, near high- water mark, this rock plane 

 is full of irregular small holes and crannies, but no loose stones or deposits, 

 other than a very thin coating of fine mud, interrupt its uniformity. 



" On this hard surface, sending their roots into the crannies, the 

 greater number of the Mangroves of Zanzibar flourish so well that a con- 

 siderable trade is carried on from Chuaka Bay in their stems. (These are 

 used in the building of all the Arab and native houses of Zanzibar, being 

 too hard for the jaws of the termites.) Only occasionally do we find 

 Mangroves growing in mud and see the demonstration of the well-known 

 method of planting, viz. by the impact of its fall forcing the root of the 

 embryo into the mud. In the majority of cases one finds the embryo 

 placed in one of the holes of the rock, which is usually of but slightly 

 Larger diameter than itself. Obviously it did not fall by chance into this 

 position ; suitable holes are not so numerous, and the insertion of the 

 radicle into them not so easy as this would imply. Moreover, I have 

 often observed embryos neatly planted in these holes at a distance of more 

 than a hundred yards from the shade of the nearest possible parent tree, 

 and in a few cases at a distance of miles. 



" How this planting could be done, except by human hands, remained 

 for a long time a mystery to me. The solution came wdien I noticed the 

 frequency with which I met embryos floating in the sea, being carried out 

 of the bay by the strong tidal currents. Often I passed through fleets of 

 tin in, as it were, all floating in the same peculiar way, viz. vertically, with 

 the leaf-bud just projecting from the water. A consideration of the shape 

 of the radicle shows that not only is there a perfect adjustment of the 

 specific gravity of the whole to that of sea-water, but a peculiar distribution 

 of it in order that the thick end may sink instead of floating uppermost, 

 as it would if the specific gravity were the same throughout. Both kinds 

 of embryo, the thick and the slender, float in the same way. On reaching 

 the shore the embryos are planted by the insinuation of the root-tip into 

 any softness 01 crevice of the bottom by the falling tide."— R. L L. 



Manures: The Relative Value of Nitrogen, Muriate, &e. 



(C.S.A. K.rp. Sili. Hatch, Mass., Ann. Rep. 1903, pp. 107 to 153; tabs.). 



