CHLOROPHYLL -GRANULES AND THE SUN'S RAYS. 377 



significance, is observed in many orchids and liliaceous plants, but on the whole 

 such a change of function in floral leaves is not common. These cursory 

 observations must show that chlorophyll may appear in all the members of a plant, 

 althougli it is also true that foliage-leaves chiefly contain the green tissue, so that 

 certainly in 90 per cent of all chlorophyll-bearing plants the decomposition of 

 carbonic acid is carried on in the foliage-leaves. 



If, now, after the description of the arrangement, form, and distribution of 

 chlorophyll-granules, we would also learn something as to how organic substances 

 are formed in the cell-chambers by means of these structures, we find ourselves 

 in the position of an inquirer who visits a chemical laboratory without a guide, 

 and wishes to ascertain in what way some material — for example, a pigment — is 

 manufactured. He notices apparatus set up there, sees the raw materials heaped 

 together, and also finds the finished jaroduct. If the manufacture is actually 

 proceeding, he can also observe whether warmth or cold and greater or less pressure 

 are brought into action as propelling forces, and he can, if intrusted with the 

 manipulation necessary to the production of such pigment, imagine the relation 

 of the difi'erent parts to the whole. Of tlie details, indeed, much must remain 

 incomprehensible, or quite unknown. Especially with reference to the quantity of 

 the transformed raw material, and with regard to the propelling forces, must the 

 visitor's knowledge remain incomplete. 



It is not otherwise with us when we would inspect the processes carried on in 

 the cells where chlorophyll-granules develop their activity. We see the eftective 

 apparatus, we recognize the food-gases and food-salts collected for working up, we 

 know that the sun's rays act as the motive force, and we also identify the products 

 which appear completed in the chlorophyll-granules. By careful comparison of 

 various cells containing chlorophyll, on the ground of observations which establish 

 the conditions under which the manufacture of organic substances succeeds best 

 and worst, having found by experience that under certain external conditions the 

 whole apparatus becomes disintegrated and destroyed; it is indeed permissible to 

 hazard a conclusion about the character of the propelling forces. But what is 

 altogether puzzling is how the active foi'ces work, how the sun's rays are able to 

 bring it about that the atoms of the raw material abandon their previous grouping, 

 become displaced, intermix one with another, and shortly appear in stable 

 combinations under a wholly different arrangement. It is the more difiicult to 

 gain a clear idea of these processes, because it is not a question of that displacement 

 of the atoms called decomposition, but of that process which is known as 

 combination or synthesis. Decompositions and analyses, even of tlie most 

 complicated compounds into simple combinations are well understood, but not 

 so the converse. It is always considered a fortunate occurrence when a chemist 

 succeeds in producing from its fundamental elements, or from the simplest com- 

 bination of these, one of those complicated bodies, which are, nevertheless, formed 

 with such ease in plant cells. When sugar is " made " in a manufactory, it is not 

 that carbon and the elements of water are used, although these are so abundantly 



