MISCELLANEOUS PLANTS 



223 



ing somewhat in form from that of the Laguncularia (L. racemosa) 

 found on both coasts of the Panama Isthmus, and, I may here add, 

 in the West Indies generally. Whether the difference is specific is 

 doubtful. The fruit of the Ecuadorian tree is more symmetrical, 

 longer and narrower, and does not broaden out into two shoulders 

 near the top as in the case of the typical L. racemosa. 



LlMNANTHEMUM HUMBOLDTIANUM, Gr. 



This aquatic plant is distributed over the warm regions of the 

 American mainland and in the West Indies. As observed in Jamaica 

 it was equally at home on the exposed muddy borders of ponds and 

 in the water. The moist seeds are globose, hairless, smooth, and 

 1-5 mm. in diameter. In the wet state about sixty-three seeds go to 

 a grain ; but in the dry state at least double that number would be 

 required to make up that weight. On account of their oily surface 

 the seeds float on the surface of a pond by throwing off the water, 

 but when completely submerged they sink. They would thus be 

 able to float for a long time in dry weather, and this would aid their 

 early germination; but the raindrops would soon sink them. The 

 seeds of our English species behave in a similar way, but here the 

 flotation is assisted by a marginal fringe of hairs. These seeds are 

 oval, flat, 4 to 5 mm. long, and have an oily surface, which 

 enables them to repel the water ; but they can be sunk by dropping 

 water on them. I observed the germinating process in both the 

 English and West Indian species. Germination usually takes place 

 in the case of sunken seeds, since from one cause or another the 

 floating seed would soon be sent to the bottom in a pond. After 

 the process is well advanced the seedling floats up and continues its 

 growth at the surface. 



The general subject of the distribution of the genus is discussed 

 in my work on Plant Dispersal. I have been familiar with these 

 plants in England, Fiji, and Jamaica, and have formed the conclusion 

 that in the tropics aboriginal man has often unintentionally assisted 

 in their dispersal. He cultivates many of his edible tubers (Colocasia, 

 Alocasia, etc.) at the borders of ponds and ditches where Limnan- 

 themums thrive. 



LUFFA ACUTANGULA, Roxb. 



This is an introduced Asiatic species to which I refer here merely 

 in connection with the slight floating power of its seeds. The seeds, 

 as tested in the well-dried condition in Jamaica, sink in a day or two. 

 Seeds of another cultivated introduced species were experimented 

 on in Fiji, and found to sink after a few days in sea- water. The 

 interest of these results lies in the circumstance that the seed of 

 Luffa insularum, A. Gray (a maritime form of L. cylindrica), which 

 grows in the Pacific islands on the shore and in the plains behind, 

 are able to float in sea- water unharmed for months, and are doubt- 

 less often dispersed by currents. This subject is dealt with on p. 426 

 of my book on Plant Dispersal. This bears on the question of the 

 connection between seed-buoyancy and a littoral station. 



