154 ARTHUR G. VESTAL. 



frequent; they are usually to be found in the habitat in con- 

 siderable numbers at any time. Frequent refers to grasshoppers 

 occurring regularly in the habitat, though not always to be found, 

 and seldom numerous when found. Occasional, occasionally 

 found in the habitat, not frequent or abundant. Infrequent, 

 not often found in the habitat. Accidental, occurring in a habitat 

 rare or unusual for the species. Specimens are usually found 

 singly and the abnormal habitat frequently adjoins one in which 

 the species is more regularly found. 



The obvious facts shown by the table are : 



1. Grasshoppers are more abundant, in species and in indi- 

 viduals, in herbaceous or grassland habitats than in forest, and 

 more abundant in dry than in moist or wet situations. 



2. Certain species are much more restricted than others in 

 range of habitats, and in accompanying range of toleration of 

 physical and vegetational factors of the environment. 



3. Although a species may be found over several associations, 

 it is more abundant in one, or two, of these, than in others 

 (Certain activities take place in more restricted habitats; chief 

 of these restricted activities is the laying of eggs.) 



4. No two plant associations have identical grasshopper 

 assemblages. 



5. No two grasshopper species have identical habit-preferences. 

 These facts and others are considered in order in the general 



discussion. 



In general, with every change of habitat there is a change in 

 the assemblage of grasshopper species. These replace one an- 

 other in 'the various habitats, often with considerable overlap, 

 but all can be arranged with respect to gradients of environmental 

 conditions. Gradients of several factors which vary together 

 may in general be said to run parallel with the development of 

 vegetation. This development of vegetation is in part the 

 result, in part the cause, of these changes of physical and vegeta- 

 tional conditions. 



The variation of environmental conditions can be expressed 

 graphically by lines representing gradients of the factors which 

 change with development of vegetation.. Environmental condi- 

 tions in each successional series may be represented by a line, 



