474 PHYSIOLOGY. 



o the latter to the entire plant. These ultimate parts of organic 

 bodies, arrived at long before we reach the limits of the possible 

 mechanical divisibility of the objects, constitute the " atoms," 

 physiologically speaking, of plants, and are called the Elementary 

 Organs. 



Under certain limitations, we may compare a plant, or an organ of a 

 plant, to a crystal. Each has its definite character by which it is possible 

 to distinguish it from any other object. But we might pulverize the 

 crystal, and yet any one fragment of sufficient size for operation would 

 display to the analyst all the chemical qualities of the entire crystal ; 

 and if we dissolved such a fragment and crystallized it upon a slip of 

 glass, we should perceive by means of the microscope that it solidified 

 into a miniature representation of the original crystal ; moreover, if we 

 then collected all the fragments and dissolved them, we might by careful 

 evaporation reproduce a crystal exactly like that from which we started. 



In Vegetables (as in Animals) the' case is entirely different. When 

 we cut a plant in pieces, the parts differ not only in form but in 

 structure, and bear no longer any recognizable relation to each other ; 

 we cannot reproduce the plant from them, and even the chemical ex- 

 amination of different fragments may give most diverse results ultimate 

 analysis alone, by which they are resolved into their mineral elements, 

 arriving at the detection of a common bond among them, that of being 

 formed of compounds which we only meet with in organic matters. Above 

 all, in the act of subdivision, although this may be carried to a high de- 

 gree in plants without destroying life (even sometimes within the limit 

 of single organs), beyond a certain point it results in the annihilation of 

 the especial force, the organizing or vital principle, by which the organs 

 were made to combine their activity to produce the distinctive character 

 as an independent individual object. 



The diversities of form and consistence of the Elementary Organs 

 give rise to all the differences of physical condition in the organs 

 of vegetation and reproduction; and all those changes which col- 

 lectively constitute the life of plants depend on the combination 

 of a multitude of minor operations which have their seat in the 

 elementary organs, singly or as combined into tissues. The study 

 of the Elementary Anatomy is therefore the only secure foundation 

 upon which to build the Physiology of Plants. 



Cells, Protoplasm. The elementary organs of plants are all re- 

 ferable to one primary type, which is not only recognizable through 

 a comparison of the fully developed modifications, but is found to 

 be the form in which all originate. This fundamental organ of 

 vegetable structure is called a Cell, and may be denned as a closed 

 sac composed of solid membrane, called the cell-wall, and filled with 

 fluid, cell-sap, and semifluid matter, called protoplasm. 



It must not, however, be overlooked that living plants and living 

 parts of plants can exist, at least for a time, without any bounding 

 cell-membrane. The perfect cell is taken, in a morphological sense, 



