215 
annual sum total of all positive temperatures for the respective locali- 
ties. The discrepancies between the above figures also show that a 
systematic influence is at work to shghtly increase the ratio for the 
northern stations, since the ratios for Poulkova are appreciably larger 
than those for Brussels. This influence, as Linsser suggests, is prob- 
ably to be found in the fact that a larger proportion of heat is con- 
sumed at the northern stations in melting the snow without changing 
the temperature, which heat is therefore lost to the growth of plants. 
The law thus discovered by Linsser is tested by him for each of the 
15 phenological stations studied in his first memoir, and not only does 
the ratio appear the same for each phase, but the slight increase as 
the latitudes increase is also confirmed, or, in other words, the ratio 
increases slightly as the annual sum total of positive temperatures 
diminishes, the increase being nothing for the first group of plants 
that blossom early in the spring and about 0.1 for the seventh group 
of plants that blossom in midsummer per diminution of 2,000° C. in 
the annual sums, 
Linsser also states this law in the following form, in which it has a 
more popular expression : 
Every individual plant possesses the ability to regulate its vital 
activity as demanded by the total heat available in its “dwelling place 
and according to the habit inherited from its ancestors, so that indi- 
viduals of the same species living in different places arrive at the 
same phase of development by utilizing the same proportions of i 
total heat to which they are accustomed. The vegetable world, 
far as we consider its vital phenomena, is indifferent to ieee 
below the freezing point. 
The preceding principle has been deduced primarily from the study 
of one phase, viz, the blossoming; but a study of the figures of the 
other phases gives a similar result, so that the method by which heat 
exercises its influence on plants is the same for all stages of develop- 
ment. 
The phase recorded as “ the falling of the leaves,” which indicates 
the approach of the winter sleep of perennial plants, is the only one 
that to a high degree depends upon the actual temperature at that 
date. 
Apparently the statement, frequently assumed as a senen al law, 
that the dates of leafing and of the falling of the leaf at the same 
place have the same temperatures is only approximately true for a 
single plant and a special locality, as, for instance, France and cen- 
tral E furope, and does not hold good for the same plant for northern 
or southern Europe. 
Linsser’s law has a most important application to the natural dis- 
semination of seeds and the acclimatization of plants. When we, 
ata given place, from year to year, see the same cycle of vegetation 
recur without changing the behavior of the plant with reference to 
the annual sum total of heat, we must conclude that the ability to 
develop itself in proportion to the total heat is transmitted from each 
