262 Transactions of the Canadian Institute. [Vol. VII. 



The supply of calcareous substance is furnished by the roots of 

 plants in the form of the bicarbonate of calcium (Roux 1900). Volkens 

 (1884) states that this bicarbonate of calcium is the chief saline substance 

 contained in the guttation drop. This is in accordance with analyses 

 made by the writer, and the view held by Van Tieghem. It is well 

 known that one of the commonest substances found in spring water is 

 calcium bicarbonate, and Roux states that the CO2 given off by the 

 roots aids in its formation. There is every reason to suppose, then, that 

 the plant obtains its calcium chiefly from this substance. It is also well 

 known that CaCOg, in the presence of CO._, and water, forms the soluble 

 bicarbonate thus: — CaC03 + C02+H20 = CaH2(C03)2 ; but, as this 

 compound is very unstable, it breaks down again if the conditions be 

 seriously disturbed. These interactions may be, therefore, important in 

 plant economy. 



The function of incrustations are (Volkens, 1884) : — (i)to keep up an 

 equilibrium between absorption of the roots and transpiration of the 

 leaves ; (2) in the excretion of useless and harmful products ; (3) to 

 prevent too rapid evaporation in a dry hot climate. Pfeffer (1897) states 

 that the function ma}- be to induce an abundant formation of dew. 

 Since calcium bicarbonate is a very unstable compound, breaking down 

 into CaCOg, CO2 and HoO, it may be, that in the formation of the 

 deposit of CaCOs, a source of supply of CO2 is suggested. The roots 

 take in the bicarbonate and it is found upon leaves of plants in the 

 morning. In the early morning when photosynthesis is becoming 

 active this bicarbonate begins to break down, resulting in a liberation of 

 CO2 which is then in demand by the plant. From these data the writer 

 assigns another probable function to these incrustations, namely, that of 

 furnishing CO2 to the plant. 



Since analyses show that the deposits from the dew-drop, the 

 guttation drop, and the water of immersion or drenching, are similar to 

 those in the calcareous incrustations, one may infer that the causes of 

 formation are similar. As the process involved in the formation is one 

 of diffusion, the loss or gain to leaves will depend upon relations exist- 

 ing between internal and external conditions. 



In summarizing the results of these discussions and experiments, we 

 may say that the resjdue obtained from the evaporation of dew-drops, 

 guttation drops, and of the water used in drenching leaves, is practically 

 the same. This residue is similar in chemical composition to that of 

 the calcareous incrustations found upon certain Saxifrages and other 

 plants. The relative proportions of the constituents, however, are 



