218 
ization to a new climate. The geographical limits of any species, 
in latitude, so far as these limits depend upon temperature alone, 
are those points at which a certain sum of positive temperatures can 
be attained between the first and the last killing frost. The northern 
and southern boundary lines of such a limiting area are the curves 
corresponding to two very different sums total of positive tempera- 
tures, the northern limit having a smaller sum and the southern limit 
a larger, beyond either of which the plant is unable to modify its 
internal organization so as to properly utilize the respective prevail- 
ing small or large quantity of heat. 
Linsser notes that different plants, especially those that blossom 
early in the year, show a strong tendency in certain years to blossom 
a second time, and he finds that when the excess of the total heat in a 
favorable year exceeds the normal annual total by a quantity equal 
to that ordinarily required for the first blossom (and this can easily 
happen on account of the small sum required for the early spring 
blossom) then the plant produces a second blossom.“ 
Tn regard to the effect of daylight as such, Linsser says the opinion 
has been expressed that possibly the duration of the daylight, which, 
during the growing period, increases as we go northward, must 
compensate for the diminishing sum total of heat; but his figures 
show nothing of this influence, since the discrepancies or departures 
between his observed and computed figures have altogether the char- 
acter of accidental errors. In fact, his law of the constant quotient or 
percentage of heat implies that the plant does not need any com- 
pensation as the heat is diminished, but directly adapts its cycle of 
operations to the diminished sum and transmits this power to all 
further generations. In addition to this, however, since the impor- 
tance of light to the plant is proven, it is necessary to remember 
that with the increasing duration of the day as we go northward 
there is a steady diminution in the intensity of the daylight because 
«Ought we not to infer from this that after a perennial plant has received 
sufficient heat to blossom and eventually to ripen its fruit it then at once begins 
to repeat this cycle of processes, and is ordinarily only delayed by the cold 
of winter? If this is true, it must be considered that with the warm weather 
of spring the plant takes up these vital processes at the point where they were 
jeft in the autumn. Therefore, in such cases, our sums total of temperature, 
moisture, ete., Should all begin to be counted with the ripening of the fruit, 
or the fall of the leaf, and not merely with the cpening of vegetation in the 
spring.—C. A. 
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