FORMATION OF CELLS FROM GUMMY FLUID. 221 



of the air, under the influence of sun-light ; at the same time, 

 a small quantity of carbonic acid is being constantly set free 

 from the whole surface, by the process of respiration, oxygen 

 being absorbed. 



354. These are the principal changes which can be detected 

 by the observer ; but there must be others of a much more ex- 

 traordinary nature, taking place within the vessels of the plant; 

 by which, from the simple elements just enumerated, those pecu- 

 liar substances are formed, which are to serve for the nutrition of 

 the structure, or are to be laid up for some yet unknown purpose 

 in its economy. Of the mode in which water and carbonic acid 

 are changed into gum or sugar, the chemist is entirely ignorant; 

 and although these are the most simple of all the extraordinary 

 conversions, which take place in the assimilation of inorganic 

 matter, he is completely unable to imitate it. There is rea- 

 son to hope, however, that he will not long remain so ; since 

 some Animal compounds have been produced by artificial 

 means. 



355. A still greater mystery is the process, by which the 

 elaborated sap is converted into cellular tissue, or any other form 

 of vegetable structure. Some parts of this process have been 

 observed, and will now be described ; but of the cause of the 

 changes, nothing is known. The young seed, before the flower 

 has expanded, is filled with a sort of sweetish mucilage, which is 

 partly composed of gum ready to become organised (. 329). 

 The first step consists in the appearance, in what was before a 

 nearly transparent fluid, of a large number of very minute gra- 

 nules. Soon afterwards, larger granules appear, round which the 

 smaller ones cluster; and they soon present a regular form, 

 resembling that of pieces of money, being flattened and circular 

 disks. On one surface of each of these, a delicate membrane is 

 seen to project, just as a watch-glass projects from the face of a 

 watch ; and this membrane gradually extends much beyond the 

 original disk, so as to form a kind of bag, in one wall of which 

 that body is included. Still, the membrane is of so delicate a 

 consistence, that it is easily dissolved away, by shaking the 

 vessel in which the process is being observed ; and it is not until 



