478 BOTANICAL GAZETTE [DECEMBER 
The evidence submitted is regarded as sufficient to prove that 
throughout a great region of Ontario dominated by Picea and Abies 
these genera are not permanent or climax forms, since they are 
replaced by Acer when soil conditions become favorable. WuitT- 
FORD (25), after studying the forests of Michigan, states that soils 
are improved by coniferous trees, and when sufficient humus soil 
has accumulated the deciduous species establish themselves. BRAY 
(5) also implies this relation. CoopEer (6), however, after a study 
of Isle Royal, comes to the conclusion that “this type (Adies- 
Picea-Betula forest) is the climax forest of that portion of the 
northeastern conifer region under consideration; in other words, 
upon Isle Royal it is the final and permanent vegetative stage 
toward the establishment of which all other plant societies are 
successive steps. It is the climatic forest of the region, permanent 
while the climate remains essentially as now.” The same paper 
records stands of Acer on certain ridges of Isle Royal and in other 
places where soil conditions seem particularly favorable. It seems 
probable that the occurrence of these stands might be a 
on the basis of soil development. 
It is evident from a study of the forests of northern Ontario that. 
the deciduous hardwood forest is encroaching upon the coniferous 
. forest region, and that the progress of this encroachment has lagged 
behind temperature changes, being now dependent principally upon, 
the rate of soil development. 
The relation of shade to the time factor of distribution is in 
accord with the specific tolerance of a given species with respect to 
light. The Acer-Picea forest provides shade which is essential 
for Acer seedlings, while detrimental to Picea or Abies seedlings. 
The encroachment of the deciduous hardwood forest upon the 
coniferous forest, made possible by changes in temperature and 
soil development, is also promoted, and the result made more 
permanent by decreasing light intensity due to shade condi- 
tions. 
The importance of methods of seed dispersal as an element of the 
time factor of distribution is obvious. Where changes in condi- 
tions are slow, for instance yearly temperature modifications, even 
the trees whose methods of dispersal allow them to migrate slowly 
