372 Vegetahle Physiology. 



framework or shell enclosing the matters in which the vitality 

 of plants appears especially to reside, the nature of the fluids 

 and solids contained in the cells and tissues must form a no less 

 essential object of investigation ; and indeed, as will be seen 

 from the sequel, the study of the cell-coidents constitutes, as 

 regards the physiologist, by far the most important branch of 

 the subject. In a practical point of view, above all, such ques- 

 tions as the history of starch and chlorophyll are of far greater 

 importance than investigations of the forms of cells, the mark- 

 ings of the spiral structures, and the like, interesting as these 

 are in other respects to the philosophic botanist. Admitting, 

 however, the paramount importance of the contents of the cells 

 in reference to the functions of vegetable life, it must not be for- 

 gotten that these are limited and defined in their manifestations 

 by the laws which rule over the forms and the arrangement of 

 the tissues, and the organs of which these constitute part. The 

 diversity of character in tlie life of different plants is principally 

 dependent upon certain fundamental differences in the plan of 

 combination of the elements (the cells). Hence it is necessary 

 at the outset of our inquiry to devote a few paragraphs to the 

 consideration of the general characters of the organization of 

 plants, before entering upon the description of the tissues and 

 cell-contents. This will enable the reader to form juster ideas 

 of the relative importance of the facts which will be afterwards 

 placed before him, by setting the whole upon a more compre- 

 hensive basis. 



The differences which we perceive in the outward characters 

 of plants are accompanied to a certain extent by differences and 

 gradations of structure in the internal parts, upon which the life 

 of the whole essentially depends. The diversities in the internal 

 anatomy of plants are far less striking than those which exist in 

 the animal kingdom, as may be naturally conceived when we 

 remember how few of the more remarkable vital functions of 

 animals are represented in plants. Moreover, the vast variety 

 existing in the vegetable world is rather dependent upon varia- 

 tions of forms and plans of arrangement {morphological types) 

 than upon physiological differences. Hence the vegetable phy- 

 siologist need not concern himself, except as to the great primary 

 groups, with the laws and " patterns " regulating the ccmfiguration 

 of the members of the different classes of plants. Leaving these 

 to the botanist par excellence^ he must especially direct his atten- 

 tion to the modifications of the tissues which are found combined 

 or distributed to a great extent irrelatively, or, at all events, occur 

 in numerous gradations within the limits of the classes whose 

 rank is defined by the plan of arrangement of their larger organs. 

 Let us endeavour to explain this a little more fully. The rank 



