230 



The values of the constants, as deduced from stations that lie in 

 the dry zone B, vary much more than those in zone A; but this is a 

 necessary consequence of the law of growth, since in such dry regions 

 the quantity of heat required to produce a given phase ceases to be a 

 simple constant and becomes a complex function of the available 

 heat and moisture and depends upon the individual ratio f/w at each 

 station. It will of course be noticed that, with few exceptions, the 

 figures in the columns of departures are negative, thereby indicating 

 that the quantities of heat actually utilized by plants in the dry 

 localities in zone B are less than the quantities utilized by the same 

 plant when it has an abundance of moisture in zone A. Most of the 

 17 positive figures among these departures relate to the period of 

 leafing, and many of them are but little larger than the limit of 

 uncertainty deduced by Linsser for the respective plants. 



All of the plants investigated by Linsser belong, as is seen by the 

 above list of names, to the exogens. They are also perennials, but 

 his intention was to extend this investigation to the herbaceous annu- 

 als, and a large mass of work in this direction had been accomplished 

 before his untimely death in 1871. 



The conclusions drawn by Linsser from the data, as summarized 

 in his published tables, may be presented as follows : 



Although the general fact above mentioned, that plants growing 

 in regions that have scant summer rains utilize less heat and less 

 moisture to produce a given phase of development than similar plants 

 having the same quantity of heat at their disposal with plenty of 

 rain during the summer, might be considered as only a further con- 

 sequence easily deduced from the principle that underlies the theory 

 of Linsser's physiological constant, yet we may also consider the fact 

 as one established empirically and seek for the most probable expla- 

 nation. Any general relation between the vital phenomena of plants 

 and their external influences can, according to the ideas established 

 in Linsser's first memoir, be looked upon either as due to temporary 

 influences or as a consequence of the habits of the plant. If we adopt 

 the former view, then the cause of the accelerated development of 

 plants in zone B will consist in the fact that from the beginning of 

 vegetation onward one or more accelerating forces have come into 

 play, the intensit}^ and duration of whose action is greater for sta- 

 tions in, zone B than in zone A. Such accelerating forces may consist 

 in a greater quantity of heat or of sunshine or possibly other influ- 

 ences. But when we come to examine the temperature curves for 

 stations in the two zones we see at once that heat alone can not be 

 considered as the stimulating force. A similar comparison shows that 

 rainfall during the growing season can not be the stimulus. Again, 

 stations such as Parma and Pessan show that great differences in 



