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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 l^etween 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." 



In 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 

 jDercentage 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 



o Ought we not to infer from this that after a perennial phint 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 

 left in the autumn. Therefore, in such cases, our sums total of temperature, 

 jnoisture, etc., should all begin to be counted with the ripening of the fruit, 

 or the fall of the leaf, and not merely with the opening of vegetation in the 

 spring. — C. A. 



