172 BOTANY PART i 



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 

 construction. The principal and most reliable source of physiological 

 knowledge is, however, obtained by experiment. 



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

 spondence 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 understanding of flowers to know that they are the 

 organs of sexual production in higher plants ; that the male cells are 

 somehow developed from the pollen formed in the anthers ; that from 

 the female cell enclosed within the ovules, after its union with a 

 male cell from the pollen-tube the embryo or rudimentary plant is 

 derived. These important facts are equally true for all flowers, no 

 matter how dissimilar they may appear. 



Physiology considers peculiarities of form in so far as they are of 

 service for special purposes arising from the relation of the plant to 

 its surroundings (Pollination, Distribution of Seeds, Water-plants, 

 etc.). This side of physiology is termed BIOLOGY, or better (ECOLOGY 

 (Bionomics) since the former term is often applied to the science of 

 living beings in general. 



The Physical and General Conditions of Life and Vital 

 Properties of Plants 



With the exception of the more or less fluid developmental stages 

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



