16 THE GROWTH OF CONFERVA IN WATER. 



from organic cells furnished from obscure sources. The process once begun, goes on 

 with uniformity and rapidity so long as external circumstances are favourable. Some 

 of the chemists of the last century asserted that no organic nucleus was required, and 

 that, on putting such bodies as spun glass or amianthus into a vessel of water, on ex- 

 posure to light, those fibres would become covered with bubbles, and the water would 

 begin to turn green. But I have found that these are experiments which do not suc- 

 ceed except under circumstances where there is every reason to suspect the incidental 

 introduction of organic matter. COUNT RUMFORD has stated that yellow silk, in an 

 unspun state, as it comes from the worm, will cause a very rapid escape of oxygen un- 

 der the influence of light. It is probable, however, that here, as in the former cases, 

 some specific organic matter has been introduced, for the result very often cannot be 

 obtained. 



41. Similar green flocks to those of which we here speak are also found on the sur- 

 faces of rocks exposed to the sea, damp walls, and other places where there is a con- 

 stant moisture. They belong to the algae or sea-weed tribe of botanists. The con- 

 fervse are thus described by Professor LINDLEY : " They consist of filaments, generally 

 simple, and are formed of two tubes, of which one, which is exterior and transparent, 

 offers no trace of organization to the most powerful eye, so that it might be called a 

 tube of glass, contains an inner articulated filament, filled with colouring water often 

 almost imperceptible, but at other times a very intense green, purple, or yellow colour." 



42. Admitting the existence of some objective germ, or sporule, or point on which the 

 light can act, we are able to give a pretty clear account of the process of evolution of 

 the green matter. When pure water is freely exposed to atmospheric air, in conse- 

 quence of the quality exhibited by all substances (Ap., 75) of diffusing into the inter- 

 stices of each other, there begin to pass into it the different gaseous bodies which have 

 access to it. These do not all pass with the same facility, nor are they taken up to 

 the same amount. The relative quantity of each follows the order of its solubility. Of 

 the three gases to which our attention must be directed in the phenomenon we are now 

 considering, oxygen, nitrogen, and carbonic acid, carbonic acid passes into the water 

 with the greatest speed, oxygen next, and nitrogen much more slowly (Ap., 54-63). 

 When a state of equilibrium, therefore, has been attained, it will be discovered that the 

 pure water has become contaminated by the presence of these different gases, and that 

 they exist in it to an amount represented by their rate of solubility. 



43. Spring water and river water, therefore, naturally contain these different gaseous 

 substances, which are intimately connected with the production of green matter. In- 

 deed, from the very mode in which rivers and springs are fed, the solution of gaseous 

 matter in them is completely secured. By the action of solar heat, vapours are rais- 

 ed from the sea, and ascending to the more elevated and cooler regions, give out their 

 latent heat, and condense into vesicles or microscopic drops, the aggregate of which 

 forms a mist or cloud. In this state of excessive subdivision, the drops are brought into 

 a perfect contact with the air, and an absorption of its constituents takes place. To 

 give still greater security, the drops of rain, which are nothing more than those vesicles 

 coalesced, as they come down from the sky pass through the subjacent aerial strata, and 



