Excurrent 



A plant with one main stem, the lower branches longer 

 than the upper, e. g., a spruce tree. 



Exempt Stock 



Livestock such as work or saddle horses and milk cows 

 which are permitted to graze on National Forests or the 

 Public Domain free of charge. 



Exfoliation 



The peeling off of material in thin layers from the sur- 

 face of rocks or the flaking off of scales or other parts of 

 organisms. 



Exoskeleton 



A hard, supportive structure in the outer part of the body 

 of many kinds of animals, e. g., shell of a crab. 



Exothermic 



Refers to the release of heat. 



Exotic 



Refers to any organism that is not native in the area 

 where it occurs; introduced, cf. Endemic, Indigenous. 



Experimental Design 



The plan of an experiment, especially to insure that the 

 data to be secured will be suitable for statistical analysis. 



Exploitation 



The ability of an organism to find, occupy, and retain 

 unused vital resources, cf. Competition, Interference. 



Exsiccata 



Dried, preserved specimens of plants. 



Exsiccation 



The process of promoting the development of desert con- 

 ditions through human activity or climatic change, cf. Sicca- 

 tion. 



136 



