CHAPTER III. 



THE GENERAL MORPHOLOGY AND PHYSIOLOGY OF 



LICHENS. 



INTRODUCTION. 

 By way of introduction to this branch of our subject it is highly 

 important to call attention to the interrelation of morphology and 

 physiology, which is of special significance in the study of the lower 

 groups of plants, fungi, lichens, and algae in particular. The in- 

 vestigator soon finds that morphological conformations of plants and 

 plant organs coincide with certain functions and, vice versa, certain 

 functions coincide with definite morphological characters of plants 

 and parts of plants. It is true that there are a number of scientists 

 who believe that morphology and physiology should be kept separate 

 for didactic purposes ; they even go farther and subdivide these main 

 divisions and endeavor to teach each subdivision as a distinct subject. 



The anatomical-physiological tendency, which received such a 

 strong impetus through the influence of Schwendener and his pupils, 

 is slowly gaining a footing in England and America. Heretofore it 

 has been customary to devote almost exclusive attention to the mor- 

 phology of plants ; the physiological significance of morphology has 

 been neglected. 



In order to avoid any erroneous conclusions as to the meaning of 

 the terms morphology and physiology an outline of their limitations as 

 employed throughout this book is given. Morphology treats of 

 macroscopical (gross anatomy, morphology in the narrower sense) as 

 well as microscopical structure (minute anatomy or histology). 

 Physiology treats of the life phenomena of cells, tissues, organs and 

 individuals. Vegetable pathology (teratology, abnormal physiology) 

 and the corresponding pathological morphology are subordinated to 

 physiology and morphology respectively. 



I. ORGANS OF ASSIMILATION. 

 I. THE THALLUS. 



The thallus is the alga-bearing assimilative portion of lichens. 

 This comprehensive definition would also include the thalloid ex- 



