118 Canadian Record of Science. 
carried in the opposite direction, the adverse influence of 
cold being far greater than that of heat, within the same 
limits. In all such cases of forced or natural migration, 
the species undergoes more or less striking and rapid modi- 
fication. Thus the alpine plant carried to a lower latitude 
or elevation, gradually loses its dwarf habits of growth and 
ultimately becomes indistinguishable from the plants native 
to the region. On the other hand, southern plants, when 
carried north, if they survive the cold of winter, grow more 
slowly and fail to attain their former height. It more fre- 
quently happens, however, especially when the ditierence 
in latitude is great, that the plant experiences important 
changes in other respects. This finds a striking illustration 
in the castor oil plant so commonly grown here on the lawn. 
A tropical plant by nature, it is in its usual habitat a per- 
ennial, which not only becomes woody, but attains the form 
and dimensions of a tree. Planted in this latitude, it at once 
becomes reduced in size, rarely exceeds six or eight feet in 
height, and remains essentially an herbaceous plant, limited 
in its growth to one season. 
On the other hand, the heat of summer, even in so high 
a latitude as this, is sufficient to bring to maturity many 
sub-tropical plants like the squash, melon and cucumber, 
which supply much needed variety to our diet. We thus 
learn that plants which, through natural means of distribu- 
tion, would find it impossible to reach high northern 
limits, on account of the extremely low temperature to be 
endured at certain seasons of the year, may nevertheless, 
through the agency of man, who plants the seed at the 
return of each spring, be maintained at very high latitudes 
or altitudes. The influence of extreme temperature thus 
indicated, is apparently a determining factor in the distri- 
bution of plants, but this can only be regarded as true when 
such extremes are severe and of long duration. 
Recognizing these facts, it is generally considered by 
botanists that the distribution of plants as a whole, is not 
determined by the extremes of temperature, but by the 
annual means. And if we follow the lines of distribution 
