215 



annual sum total of all positive tcnipeiatiiros for the respective locali- 

 ties. The discrepancies between the above figures also show that a 

 systematic influence is at work to slightly 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 j^roportion of heat is con.- 

 suuied 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 whicii 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 difl'erent places arrive at the 

 same phase of development by utilizing the same proportions of the 

 total heat to which they are accustomed. The vegetable world, so 

 far as we consider its vital phenomena, is indilferent to temperatures 

 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 b}^ 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 temjicrature at that 

 date. 



Apjjarently the statement, frequently assumed as a general law, 

 that the dates of leafing and of the falling of the leaf at the same 

 place have the same tenii)eratures is only a})pr()ximately true for a 

 single plant and a special locality, as, for instance, France and cen- 

 tral Europe, and does not hold good for the same jilant 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, 

 at a given place, from year to year, see the same cycle of vegetation 

 recur without changing the behavior of the plant with rx'ference 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 



