265 
[Shaler. 
1891.J 
ly do these animals convey the nuts to a distance of more than 
two or three hundred feet from the point where they find them. 
I think it probable that the average dissemination of seeds brought 
about in this manner is not more than a hundred feet from the 
foot of the tree on which the nuts are borne. It seems to me that 
even two hundred feet is an excessive estimate, for in most cases 
the little animals properly economize their labor by storing their 
winter’s supply as near as is convenient to its source. 
We have last to notice the method of diffusion which is ac- 
complished by the processes of the tree itself ; this, which we may 
term the organic process of dissemination is brought about by the 
growth from the seed to the tree : in the case of our walnuts and 
hickories it requires about twenty-five years to bring the plant 
into the condition of development where it may in turn produce 
seed. At this age the branches of the tree may be computed as 
extending about 30 feet from the position of the trunk in a hori- 
zontal direction. Dropping from the extremities of these 
branches, the seed slightly affected in their falling by the action 
of the wind, may come to the ground at an average maximum 
distance of fifty feet from the place of the bole. My observations 
of walnut and hickory trees appear to indicate that fifty feet from 
the trunk of a plant which is a quarter of a century old is 
about the maximum of diffusion by this method. 
With these considerations in mind, and let us note the facts 
concerning the distribution of these large seeded trees in the re- 
gion to which they have won their way since the close of the 
glacial period. Without entering into the detail concerning the 
distribution of these forms in the drift covered district, a task 
which cannot be accomplished until we know more exactly than 
we now do the distribution of these large seeded trees, we may 
assume it as certain that our black walnut and our pignut hickory 
have between western Minnesota and the Atlantic coast, on the 
average, advanced for the distance of about 400 miles to the north 
of the ancient ice front whereunto their ancestors were driven by 
the presence of the glacial sheet. In the valley of the Mississippi 
the average length of this northern journey is probably near 600 
miles. Counting it, however, as the lesser distance, let us see 
how far it seems possible to effect this transportation by other 
actions than by the growth of the tree itself. In the first place 
we observe that transportation by rivers may be practically ex- 
