xii INTRODUCTION. 



and to exercise the functions of the parent plant cell, with 

 which they remain permanently united. Thus, in the nume- 

 rous tribes of marine Cryptogamia or algae, the endochrome 

 (sv8ov within, and zpupa, a color) is diffused through the entire 

 substance of the frond, so that the whole plant presents the 

 same color in all its parts, and the reproductive matter, or 

 sporules, makes its appearance in many species, ^indifferently 

 on any or every part of the plant. 



In the Phanerogamia, or flowering plants, on the other hand, 

 root, stem and leaves are separate, well-defined organs. 

 From the first commencement of germination there is a stem 

 more or less manifest, and a tendency to develope in two oppo- 

 site directions, into the earth and atmosphere, the two grand 

 sources from whence these plants obtain the materials of their 

 growth or enlargement. To subserve the purposes of a higher 

 and more elaborate nutrition, certain cells of the parenchyma 

 are carried to a much higher degree of development, and 

 assume the form of woody fibre and spiral vessels. 



The pleurenchyma of flowering plants (26) becomes more 

 distinctly marked in their leaves, as organization advances in 

 complexity of structure, until at length, in the most highly 

 organized plants, its fibres form a beautiful anastomosis of 

 veins, veinlets and capillaries. The leaves of Thalictrum 

 anernonoides, the rue-leaved anemone, an early and exceed- 

 ingly abundant spring flower, furnish an admirable illustration 

 of pleurenchyma thus ramified and attenuated. 



But throughout organic nature, a change in the form of any 

 organ is always associated with a corresponding change in its 

 function. The secretion of the cells is therefore no longer 

 uniform, but varied and well defined in its character, certain 



