6 CONCEPT AND HISTORY. 



formations and their effect upon it. To determine the exact character of each 

 of these agencies independently is a work of no little difficulty; and then to 

 compare and combine their respective influences upon vegetation presents 

 very great additional difficulty. But the experiments of nature furnish us in 

 the native flora a practical correlation of them. The native vegetation there- 

 fore merits careful consideration, none the less so because it is rapidly disap- 

 pearing, and a record of it will be valuable historically. 



" It is rare in nature that a single plant occupies exclusively any considerable 

 territory, and in this respect there is an important difference between nature's 

 methods and those of man. The former raises mixed crops, the latter chiefly 

 simple ones. But in nature, the mingling of plants is not miscellaneous or 

 fortuitous. They are not indiscriminately intermixed with each other without 

 regard to their fitness to be companions, but occur in groups or communities, 

 the members of which are adapted to each other and their common surround- 

 ings. It becomes then a question of much interest and of high practical 

 importance to ascertain, within the region under consideration, what are the 

 natural groupings of plants, and then what areas are occupied by the several 

 groups, after which a comparison with the soils, geological formations, surface 

 configuration, drainage and climatic influences, can not fail to be productive 

 of valuable results. 



"The following natural groups are usually well marked, though of course 

 they merge into each other where there is a gradual transition from the condi- 

 tions favorable for one group to those advantageous to another. In some 

 instances it is unquestionably true that other circumstances than natural 

 adaptability control the association of these plants, and an effort has been 

 made in the study of the region, to discern these cases and eliminate them 

 from the results, so that the groups that are given here are believed to be 

 natural associations of plants. Their distribution is held to show in what 

 localities conditions peculiarly advantageous to them occur, and hence advan- 

 tageous to those cultivated plants that require similar conditions." 



The author has used both class and group as synonyms of community, but 

 the latter term is substituted in the following list for the sake of clearness: 



A. Upland vegetation. B. Marsh vegetation. 



(1) Herbaceous. 10. Grass and sedge community. 



1. Prairie community. 11. Heath community. 



(2) Arboreous. 12. Tamarac community. 



2. Oak community. 13. Arbor vitae community. 



3. Oak and maple community. 14. Spruce community. 



4. Maple community. C. Communities intermediate between 



5. Maple and beech community. upland and marsh. 



6. Hardwood and conifer community. 15. Black ash community. 



7. Pine community. 16. Yellow birch community. 



8. Limestone ledge community. 



9. Comprehensive community. 



Merriam, 1898. — In "Life Zones and Crop Zones," Merriam summarized the 

 experiential evidence as to the climatic indications for crop plants. This was 

 arranged in relation to seven life zones based theoretically upon temperature, 

 but determined for the most part by the distribution of native plants and 

 animals. As a pioneer attempt to organize a vast field, it deserves great credit, 

 even though later studies have rendered his zonal classification of secondary 

 value. The author's understanding of the nature and scope of climatic indi- 

 cators is best shown by the following excerpts: 



"For ten years the Biological Survey has had small parties in the field 

 traversing the public domain for the purpose of studying the geographic dis- 



