160 BOTANY 



form and function. But, in all plants, those organs to which the 

 same functions are assigned have assumed the form most efficient 

 for their purpose ; so that, for example, the leaves and roots of plants 

 otherwise most dissimilar are constructed on the same general plan. 

 In proof of this may be cited the general terms leaf, root, stem, and 

 flower, the comprehensiveness of which is even more evident in popular 

 speech than in the technical language of Botany, which has given to 

 these terms a more strictly defined and limited meaning. 



Similarity in the appearance and structure of organs indicates the 

 exercise of common functions and duties ; while dissimilarities in the 

 form and structure of different organs — such as the leaf and root — are 

 indicative, on the other hand, of their different utility to the plant. 

 There lies, then, in the morphological and anatomical development of 

 an organ an unmistakable proof that it exists because of its function, 

 and that it is not of accidental origin. 



The attributes and functions of organs, as well as of single cells, are 

 the subjects of physiological study. It is evident, however, that such 

 study must be based upon an intimate knowledge of the outer and 

 inner structure of plants ; just as the working and efficiency of a 

 machine first become comprehensible through a knowledge of its con- 

 struction. On the other hand, the study of external and internal 

 Morphology becomes animated by Physiology, and attains thereby a 

 deeper purpose and meaning. 



It is the province of Physiology to discover the points of correspond- 

 ence among the numerous individual phenomena, and to bring to light 

 such as possess an essential functional significance. On the other hand, it 

 is the variations, or family peculiarities, which are of value in Systematic 

 Botany, since from them a knowledge of family relationships may be 

 derived. For example, it suffices for the physiological conception of 

 flowers to know that they are the organs of sexual reproduction in 

 higher plants ; that the male cells are somehow developed from the 

 pollen formed in the anthers ; that from the female cells enclosed 

 within the ovules, after their union with male cells, the embryos or 

 rudimentary plants are derived. These important facts are equally 

 true for all flowers, no matter how dissimilar they may appear. 



The Physical and Vital Attributes of Plants 



With the exception of the more or less fluid developmental stages 

 in some of the lower organisms, as in Amaba or the plasmodia of 

 Myxomycetes, plants, in spite of the great amount of water contained 

 in them, are of the nature of solid bodies. As such they possess in 

 common even with inanimate objects the physical attributes of weight, 

 density, elasticity, conductivity for light, heat, electricity, sound, etc. 

 Important as these attributes are for the very existence and continu- 

 ance of the life of a plant, they do not constitute that life itself. 



