1895.] The Philosophy of Flower Seasons. 115 
duced plants seem to flourish much more prosperously than 
the natives, and this is explained as owing to the fact that in 
a new country they escape the competition of forms which have 
been constantly undergoing modification to hold them in 
check. Many of our introduced plants, however, are not char- 
acterized so much by: the facility with which they crowd out 
native species as by their habit of adjusting themselves to con- 
ditions induced by man, and of filling places rendered by him 
unoccupied; and in this work many of them no doubt have 
undergone a course of selective training in older lands. But 
it is sufficient for our purpose to start with the fact that intro-. 
duced plants are to a great extent relieved from the pressure 
of competition which holds among the indigenous plants, and, 
therefore, as regards blooming, would be expected to flower 
longer. And this isin fact the rule. In those generain which 
we have both indigenous and introduced species the formér 
bloom for a short time (Sisymbrium canescens, Stellaria longi- 
Jolia, Cerastium nutans, sunflowers, “thistles) while their intro- 
duced congeners bloom much longer (Sisymbrium officinale, 
Stellaria media, Cerastium vulgatum, Helianthus annuus, Cnicus 
lanceolatus). The introduced species of Cruciferae, Caryophylla- 
ceae, Portulacaceae, Malvaceae, Leguminosae, Umbelliferae, 
Compositae, Scrophulariaceae, Labiatae and Polygonaceae 
present cases of long blooming which are not cs by any 
‘native species of the respective families. 
Some native plants which have a strong tendency to occupy 
waste grounds also show a tendency to bloom for a long time. 
A similar disposition is manifested in the cases of plants hav- 
ing small flowers infrequently visited by insects and often self- 
pollinating. Many originally aquatic plants and others which 
have been forced to take to the water are, like introduced 
plants and the degraded entomophilous flowers, relieved from 
the severer competition of terrestrial plants and in a similar 
way show a tendency to prolong their blooming periods. 
In the case of the indigenons flora there is a well marked 
disposition to limit the blooming period in anticipation of the 
advancing winter. The direct effect of cold is not obvious, 
but there is an evident tendency not to prolong the period 
