88 SYSTEMATICAL BOTANY. 



646. Those peculiarities of structure which are connected 

 with the manner in which a plant is developed are physio- 

 logical. 



647. Those peculiarities of structure which are connected 

 with the manner in which parts are arranged are structural. 



648. Physiological characters are of two kinds; 1, those 

 which are connected with the mode of growth (or organs of 

 vegetation), and, 2, those which regulate reproduction (or 

 organs of fructification). 



649. Physiological characters are of greater importance in 

 regulating the natural classification of plants than structural. 



650. All modifications of either are respectively import- 

 ant, in proportion to their connection with the phenomena of 

 life. 



651. If we allow ourselves to be steadily guided by these 

 considerations, we shall find that the internal or anatomical 

 structure of the axis, and of the foliage, is of more importance 

 than any other character. 



Because these are the circumstances which essentially regulate the functions of 

 growth, and the very existence of an individual. 



652. That next in order is the internal structure of the 

 seed, by which the species must be multiplied. 



Thus the presence of an embryo, or its absence, the first indicating a true 

 seed (531), the latter a spore (590), are most essential circumstances to con- 

 sider. And so also the existence of albumen in abundance round the embryo, 

 or its absence, must be regarded as a physiological character of the highest 

 value : because, in the former case, the embryo demands a special external 

 provision for its early nutriment, as in oviparous animals ; while, in the latter 

 case, the embryo is capable of developing by means of the powers resident in 

 itself, and unassisted, as in viviparous animals. 



653. Next to this must be taken the structure of the organs 

 of fructification, by whose united action the seed is engen- 

 dered ; for without some certain, uniform, and invari- 

 able action on their part, the race of a plant must become 

 extinct. 



Thus we find that the structure of the anthers, placenta?, and ovules, are more 

 uniform than that of the parts surrounding them ; while their numbers are 

 variable ; and the condition of the filament, which appears of so little import- 

 ance in a physiological point of view, is also inconstant. So also the texture 

 and surface and form of the pericarp, which acts as a mere covering to the seeds, 

 is not to be regarded in these inquiries, and, in fact, differs from genus to genus ; 

 as, for instance, between Pyrus and Stranvaesia, or Rubus and Spiraea, in the 

 truly natural Rosaceous order. 



