288 SCOTTISH GEOGRAPHICAL MAGAZINE. 



species at the south end of Lake Winnipeg. The existence of the white 

 cedar at this particular locality, so far removed from its general limits, 

 may have been rendered possible by a combination of conditions such as 

 the required soil, moisture, warmth, etc., which may not be all united at 

 any intermediate locality ; or perhaps some better explanation may be 

 found to account for this singular outlier. 



Perhaps it is due to human agency, as the Indians often carry cedar 

 boughs in the bottoms of their canoes as a lining, for which purpose they 

 are very suitable on account of their flatness. It is probable that if care 

 were taken to plant the cedar in suitable situations, it would be found to 

 grow at almost any other locality on the western side of Lake Winnipeg, 

 for it appears probable that this and some other species of our trees 

 have not yet reached in all quarters the limits of their possible extension 

 from the southward ; in other words, it is not by any means certain that 

 the present limits of all our trees have become permanently established. 

 Some of them may be still slowly progressing from the southward in one 

 part, and possibly retreating in another, or some may be advancing or 

 retiring all along the line. 



The slow rate at which most kinds of trees have spread themselves 

 over the country is evidence, either that more than 10,000 or 20,000 

 years have elapsed since the glaciers retired from their most southern 

 extension to the Arctic regions, or that they were never confluent across 

 the greater part of the intervening country. 



MEANS FOR THE DIFFUSION OF TREES. 



The seeds of some kinds of trees are endowed with much better means 

 of transportation than others, as, for example, the down of the poplar 

 seeds and the wings of those of the conifers, and hence such species 

 may have reached the utmost limits of their possible growth. Some 

 species are prolific in individual trees, while others are nowhere common, 

 being only sparingly scattered in all parts of their area of distribution, 

 and as they produce proportionately less seed, they will make slower 

 progress in occupying new ground. With some species "seed years" 

 occur seldomer than with others, and this is another cause of dis- 

 parity in the rate of dispersion of different species. The number of 

 seeds produced by some of the nut-bearing trees is extremely small com- 

 pared with that of most others, and no provision is made for scattering the 

 nuts by the wind. But other means are not wanting, and one of the most 

 interesting is that of the squirrels and the birds of prey. It is a 

 common thing for a squirrel, when running off with a nut to a distance 

 from the parent tree, to be attacked by a hawk, when he will immediately 

 drop his burden to facilitate his escape, and this nut may have an 

 opportunity to germinate the following spring. Again, if he should fall 

 a prey to the bird, all the " caches " of nuts which he has made in the 

 ground may grow the next year. 



OUTLIERS OR COLONIES. 

 The following may be mentioned as examples of the known outliers or 



