I50 STUDIES IN SEEDS AND FRUITS 



been dried in air, to the plant that has died spontaneously, and 

 to the plant that has been subjected to almost absolute desicca- 

 tion by heat and other means, all ultimately reaching the same 

 condition of equilibrium with regard to the atmosphere. 



We will illustrate Berthelot's principle by combining in 

 one statement the results of his different experiments. 

 Portions of a living grass, a species of Festuca^ weighing, we 

 will suppose, lOO grammes, are allowed to dry in the air of an 

 ordinary room for some days, until they acquire a stable weight 

 affected only by the usual small hygroscopic fluctuations. 

 Their weight is thus reduced by loss of water to about 66-^ 

 grammes. They are then exposed to a temperature of iio° 

 C. for some hours, with the result that the weight is further 

 reduced to 6i grammes. After being laid aside for some days, 

 the material, by the absorption of moisture from the air, returns 

 to the original air-dried weight of about 66' c, grammes, and 

 there remains, varying slightly with the changing humidity of 

 the atmosphere. It is in the ^^ grammes which the air-dried 

 material lost in the oven and regained when subsequently 

 exposed to the air that the secret of the hygroscopicity of 

 plants lies. 



Table illustrating Berthelot's "Principle of Reversibility." 

 (The Results of Different Experiments are here combined, 

 the Materials employed being Portions of a Species of 

 Festuca.) 



Note. — The data representing the effect of exposing fresh and air-dried material to a 

 temperature of iio° C. belong to the same experiment, the rest of the data being supplied 

 from the indications of other experiments. 



