VI CONTENTS. 



SECTION IV. 



The Morphology and Physiology of Lichens ... 39 



I. The Thallus 39 



1. The Cbdstose Type 41 



2. The Foliose Type . -. 42 



3. The Fbuticose Type 44 



II. The Apothecia 45 



1. The Fungal Type 46 



2. The Thalline Type 47 



III. Accessory Structures 48 



1. The Soredia 48 



2. The Cyphell-e 49 



3. The Cephalodia 50 



4. The Spermagonia 50 



SECTION V. 



The Occurrence and Distribution of Lichens ... 52 



I. The Latitudinal and Altitudinal Distribution 



OF Lichens 52 



SECTION VI. 



Lichens and the Naturalist 56 



I. The Collection of Lichens 56 



II. The Study of Lichens 63 



III. The Pbesebyation of Lichens 65 



PART II. 

 The Systematic Study of Lichens. 



SECTION I. 

 Systems of Classification 73 



SECTION II. 



Keys to the Study of Lichens 76 



I. Artificial Kky to the More Important Genera 



OCCUBBINQ IN THE UNITED STATES ... 77 



II. Natural Key to the Families 80 



