MISCELLANEOUS PLANTS 



179 



the Anon a trees, when within a distance of five or six miles from the 

 coast, blend with an outer zone of cypress swamp. In other places 

 where they approach the coast they are associated with Rhizophora 

 mangle, in others, again, they largely form hammocks, or groups 

 of trees., that rise up like islands in the midst of the marsh vegeta- 

 tion of the Everglades. One of the characteristic developments of 

 the tree occurs in the Banana Holes., which are shallow depressions 

 or sinks, in which water often collects., where flourish a variety of 

 other plants. Chrysobalanus icaco, Cladium, Phragmites, Sabal. Sagit- 

 taria, Salix. Typha, etc. 



From what has been said it would thus appear that in South 

 Florida this tree has many associates of a very different kind, and 

 we may regard its behaviour there as the story of a tree of the man- 

 grove formation that has been endeavouring for ages to gain for itself 

 an inland station. 



As regards the modes of dispersal of Anona palustris it is likely, 

 as suggested by Prof. Harshberger (p. 116).. that the seeds are locally 

 distributed by frugivorous birds. He also adopts the suggestion of 

 Dr. Safford that it is distributed by its light, corky wood, fragments 

 of the tree being carried by water. Observation and experiment 

 will show whether this last mode of dispersal is effectual. However, 

 a very effective method of dispersal came under my notice in the 

 Guayas estuary in Ecuador, a method described ten years ago in 

 my book on Plant Dispersal (pp. 488-9). Very frequent in the 

 floating drift of the river off Guayaquil were the seeds of this tree, 

 often in a germinating condition. The seeds were liberated by the 

 decay of the floating fruit, which was also common in the river-drift. 

 They occurred commonly amongst the materials afloat in the Gulf 

 of Guayaquil, ten to twenty miles off the mouth of the estuary, 

 and were washed up on the beaches thirty miles to the south. Ex- 

 periments showed that the seeds will float in sea-water until they 

 rot and decay — one experiment covering eleven weeks, none of the 

 seeds sinking, though several had become putrid. Seeds from 

 Ecuadorian and Jamaican trees behaved in the same way. 



The tendency of the seeds to germinate whilst afloat in rivers 

 raises an objection against their fitness for dispersal by currents, 

 since sea-water would probably kill the germinating seed. Here a 

 good deal depends on whether the small embryo has begun its growth 

 within the albumen before the seed reaches the sea. In the resting 

 condition the embryo is only about one-sixth of the length of the 

 nucleus of the albumen, which is about 11 mm. long, and the cotyledons 

 are minute. Considerable growth of the cotyledons takes place 

 within the seed at the expense of the albumen before the tip of the 

 radicle protrudes : and ultimately the cotyledons occupy almost 

 the length and breadth of the seed nucleus. It is therefore apparent 

 that a great deal depends on whether the embryo has passed beyond 

 the resting-stage before the seed reaches the open sea. When the 

 embryo is about one-third of the length of the nucleus, the tip of 

 the radicle, which abuts against the pervious hilar end of the seed, 

 has for its sole protection a thin membranous layer of albumen. 

 In the resting seed, the embryo is better protected by the albumen 



