22H 



iiial pliuits of toiiipcinlr rciiioiis, which arc lh()>c coiisulcrcil in his 

 second memoir. So he h'aves the stiuly of atmospheric vapor and 

 plant life to the future, while confining himself at present to the 

 relation between rai:ifall and the periodic phenomena of vegetation. 



It is not necessary to reproduce the tables of normal monthly rain- 

 fall given by Linsser for each of his stations, and generally based 

 upon many years of observations. Of course, these numbers express- 

 ing the local rainfalls are, as is well known, less directly applicable 

 to a neighboring locality than are the mean monthly temperatures, 

 and they must l)e used with correspondingly less confidence. 



The constant fractional part of the annual sum total of heat, as 

 previously established by Linsser. afforded him a valnable suggestion 

 or a working hypothesis as to the relation between the life of the 

 plant and other factors, such as sunshine, rainfall, nutrition, and in 

 fact every factor that influences the life of the plant. If, namely, a 

 plant utilizes one-tenth of its annual cycle of heat in order to bring 

 it to the leafing -stage, why may it not also require one-tenth of its 

 annual cycle of rain or sunshine or some similar constant fractional 

 part ? Xow. in the development of a plant there is necessary, first, the 

 material, viz, rainfall, or irrigation water with the nutrition con- 

 tained therein, and on the other hand one or more forces, such as 

 sunshine and heat, by the help of which the plant can utilize that 

 material in its process of assimilation. The different phases of the 

 development of the plant, such as the appearance of the blossoms 

 and the ripening of the fruit, are work accomplished; in this work 

 the water supplies the principal material, while the heat, says Linsser, 

 plan's, the role of the principal force; but the work of the plant — that 

 is to say, its progressive development — will onl}^ be in proportion to the 

 force, so long as the latter finds a sufficient quantity of material present 

 to insure the complete utilization of the force. Evidently a force that 

 is competent to convert a certain quantity of material to the use of 

 the plant will only be half utilized if only half of this quantity of 

 material is present. In other words, the development of the plant 

 goes on in proportion to the quantity of heat only so long as the plant 

 has at its disposal the maximum (juantity of material that can be 

 worked over by this heat. 



Therefore any further investigations as to the relation of the life 

 of a plant to its external factors must necessarily consider the dis- 

 tribution of material with reference to the distribution of heat. In 

 our present case it is the distribution of the quantity of rain with 

 reference to the heat, and if such relative distribution is not considered 

 then its omission is only permissible under the assumption that dur- 

 ing the whole period of vegetation the material necessary to the 

 growth of the plant is ahvays present in such quantity that at any 



