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 
lus 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 
‘ain 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 asa 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 onwafd one or more accelerating forces have come into 
play, the intensity 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 
° 
