248 TIMBER AND SOME OF ITS DISEASES. [CHAP. 



sulphuric, and phosphoric acids, as well as a little 

 common salt, and traces of one or two other things. 

 It is, in fact, of the nature of ordinary drinking water, 

 which always contains minute quantities of such 

 salts : like drinking water, it also contains gases 

 (oxygen, nitrogen, carbon-dioxide) dissolved in it. 



It follows from what has been said that the cell-sap 

 tends to accumulate small increasing quantities of 

 these salts, &c., as the water passes away by evapora- 

 tion. But we must remember that the living contents 

 the protoplasm, nucleus, and the green chlorophyll- 

 corpuscles use up many of these salts for their life- 

 purposes, and other portions pass into the cell-walls. 



It will thus be seen that the green chlorophyll- 

 corpuscles are bathed by a fluid cell-sap, the dissolved 

 gaseous and mineral contents of which are continually 

 changing, even apart from the alterations which the 

 life-processes of the living contents of the cell them- 

 selves entail. We may say that the chlorophyll- 

 corpuscles find at their disposal in the cell-sap, with 

 which they are more or less in direct contact, traces of 

 salts, oxygen, carbon-dioxide, and of course water, 

 consisting of hydrogen and oxygen. 



Now we have the best possible reasons for knowing 

 that some such changes as the following occur in these 

 chlorophyll-corpuscles, provided they are exposed to 



