ZOOLOGY AND BOTANY, MICROSCOPY, ETC, 771 



as, for example, when yeast produces carbonic acid witliout the 

 presence of free oxygen, decomposing the sugar with production of 

 alcohol. 



4. Insulation-resjnration. This is a process of evolution of oxygen, 

 which takes place in the decomposition of vegetable acids, and is 

 possible only under the influence of light. 



The following four kinds of metastasis may also be distin- 

 guished : — 



1. Dissociation includes those processes which result in a definite 

 decomposition of any substance into several compounds, as when the 

 proteids of protoplasm are decomposed into a nitrogenous and a non- 

 nitrogenous substance. 



2. Association. This takes place when certain nitrogenous and 

 non-nitrogenous substances unite to form proteids. 



3. Decomposition. A typical instance of this occurs in the disap- 

 pearance of starch in the germination of seeds ; it is always associated 

 with normal respiration. 



4. Metamorpliosis. This is not connected with the complete 

 decomposition of organic compounds, the resulting organic com- 

 pounds being nearly related to those from which they are derived ; 

 as, for example, when dextrine is converted into glucose. No process 

 of respiration, except the second, can take place in connection with 

 metamorphosis, but it includes certain processes of oxidation con- 

 nected with the fatty acids. 



The substances which are employed in the building up of 

 organized vegetable structures, such as cellulose, starch-grains, pro- 

 teids, &c., whether directly or in connection with metastatic processes, 

 may be termed plastic substances. To those metastatic processes 

 which yield products that have no direct relation to the processes of 

 growth in the vegetable organism, the term degradation-products may 

 be applied. Mucilage is, for instance, a degradation-product of 

 cellulose and starch. 



The remainder of the paper is occupied with a discussion on the 

 behaviour of proteids in metastasis, and of the phenomena of respi- 

 ration and fermentation. The latter the author regards as a true 

 process of dissociation, not necessarily connected with the presence of 

 a so-called " ferment." 



Hydrostatic Tension as a Cause of Movements of the Sap and of 

 various Organs.* — The formation of cushions at ligatures and at 

 spots of the stem which had been decorticated, is usually ascribed to 

 the action of a descending sap. M. A. Barthelemy has been unable 

 to obtain direct evidence of the existence of such a descending 

 current ; the actual facts point rather to a lateral force. The ascend- 

 ing current of sap is determined by the suction of the roots, and by 

 the evaporation and fixation of water on the surfaces of the leaves ; 

 the reverse movements being due to the cessation of evaporation and 

 the reaction which results. 



The phenomena of heliotropism, and the movements of the leaves 



* Comptes Eendus, xcii. (1881) pp. 1121-3. 



