DIV. I .MORPHOLOGY 165 



2. Adaptations of the Cormus to its Mode of Life 

 and to the Environment C 84 ) 



The form and structure of the corrnus are closely connected with 

 its mode of life, which in turn depends on the environment. Practi- 

 cally all plants thus appear adapted to the environments in which 

 they are usually found. The uniform physiognomy exhibited by the 

 plants of any locality, as well as the differences in the physiognomy 

 of the vegetation in localities which differ in climate, depend upon 

 this. The vegetative organs are therefore not typically constructed 

 in all cormophytes, but are frequently altered or metamorphosed in 

 a variety of ways. Very careful developmental or anatomical investiga- 

 tion may be required to show that the variously-constructed organs 

 of many cormophytes are derived by the metamorphosis of the three 

 primary organs, root, stem, and leaf, and to ascertain with which of 

 these any particular structure is really homologous. The external 

 form and the functional activity of mature organs may be very mis- 

 leading. One organ may assume the form and functions of another, 

 e.g. a stem resembling a leaf ; different primary organs may take on 

 the same forms in relation to performing the same functions and thus 

 be analogous but not homologous. As a rule, however, when all the 

 characters of an altered organ are taken into consideration, some will 

 leave no doubt as to its morphological origin. 



The form of a plant and of its parts is determined in the first 

 place by its mode of nutrition. Thus there are striking and important 

 morphological differences between cormophytes which require only 

 inorganic food materials (AUTOTROPHIC PLANTS) and those which 

 require organic food (HETEROTROPHIC PLANTS). 



A. Autotrophie Cormophytes 



The green plants are structurally adapted to autotrophic life. The 

 typical features of the construction of autotrophic cormophytes have 

 been described above. The green cormophytes may exhibit consider- 

 able variety among themselves, for their structure is adapted to the 

 different features of the environments in which they occur. 



Among the numerous factors in the differing external conditions 

 WATER and LIGHT have by far the greatest influence on the form of 

 green plants. This is evident, for the plant can only carry on its 

 life when sufficient water is available, and only when there is sufficient 

 light can it construct organic substance from inorganic food materials 

 and thus be autotrophic. 



(a) Adaptations to the Humidity of the Environment 



1. Water Plants. Hydrophytes ( S5 ). Special peculiarities in 

 structure are found in plants which live in water. These can 



