108 MASSACHUSETTS HORTICULTURAL SOCIETY. 



resistant to the action of salt water. The pahn whieii bears it fre- 

 quents the sea margin, and the fruits falling into the water are 

 carried immense distances by the action of winds and currents. 

 Hence the coco palm is one of the first plants to appear upon coral 

 islands, and it has even been said to be the only palm tree common 

 to both hemispheres. Again, there are certain species of which the 

 seeds or fruits have developed plumes or tufts of fine hairs which 

 make the total bulk of the seed or fruit very large in proportion to its 

 weight, thus enabling the wind to carry it very long distances. 

 Such is the case with many Composita?, as for instance the dande- 

 lion, the plumose fruit of which is known to everybody. This can 

 be carried by the wind for hundreds of miles, and hence is widely 

 scattered over North America and Europe, and very probably much 

 beyond these limits. And many other instances of a like character 

 could be cited. A most interesting and important branch of this 

 inquiry is concerned with the natural return of plants to localities 

 from which climatic changes have driven them. Thus the glacial 

 ice-sheet drove all plants before it to the South, but when it in turn 

 retreated back to its home in the frozen North, these plants tended 

 to follow it and re-occupy their old haunts. Now there is every 

 reason to believe that those plants having methods of rapid dissemi- 

 nation and therefore an advantage over their less fortunate relatives, 

 travelled more quickl}' and occupied the ground, and that the slower 

 moving forms are still with ditticnlty making their way back whence 

 they came. This seems to be well illustrated by the trees. The 

 forms which have light-winged seeds easily scattered b}^ the wind, 

 such as birches and willows, extend very far north, and the same is 

 true in lesser degree of the elms and maples. But the heav}^ seeded 

 trees like beeches, oaks, chestnuts, etc., are not so far advanced as 

 their constitutions will allow, and they are slowl}' but steadily 

 moving north, a point which is well argued by Professor Shaler of 

 Cambridge. And the extremely different rate of the natural spread 

 in this way of the various species, when a new land connection is 

 formed with another district, must be taken into account in all these 

 studies. 



Another method of securing dissemination, of wide prevalence and 

 effectiveness, is found in those fruits which by bright colors are 

 made conspicuous, and by juicy pulp palatable to birds or animals — 

 a very large class, including nearly all of our edible fruits. In such 

 cases the seeds are swallowed Avith the fruit and being provided 



