46 The Plant World. 



of Maryland, which is treated in its general descriptive phases," 

 and (p. 29) that "together with the scientific aim of presenting 

 a picture of the vegetation of Maryland and its distribution, the 

 present work has been carried on with a view to discovering 

 relations between the natural vegetation and the crop possibili- 

 ties of definite areas." 



The Ecological Plant Geography of the Atlantic States is 

 especially interesting in the latitude of Maryland, and applies 

 in a way to all territory between Pennsylvania and Georgia. 

 In all this region one finds the coastal plain, the Piedmont and 

 the Mountain zones, each with distinctly different soils and cli- 

 matic conditions whose difference is indicated at least by data 

 in this paper showing a mean difference of 115 days between the 

 length of the growing season in the tidewater section and that 

 of the Alleghany Mountain section. (For method of determina- 

 tion, see p. 39). The study of the vegetation was taken up and 

 is described according to these natural divisions of the state. 



The plan of the work is as follows: I. Introduction; II, 

 The Floristic Plant Geography of Maryland; III. The Ecological 

 Plant Geography of Maryland; IV. The Relation of Natural 

 Vegetation to Crop Possibilities; V. The Agricultural Features 

 of Maryland; VI. The Forests and their Products; VII. List of 

 Plants Collected or observed. 



Dr. Shreve evinces, more than does any other student of 

 Ecological Plant Geography with whose writings I am familiar, 

 the modern idea of the soil as a dynamic and not a static system. 

 Starting with the fact that soils are derived from rocks which 

 almost invariably contain such a variety of chemical elements 

 that the derived soils yield all the inorganic substances necessary 

 for the support of plant life, he proceeds to show how the differ- 

 ences in the vegetation on them may be traced to the operation 

 of dynamic, meteorologic and biological agencies. Also that the 

 presence and kind of soil water are expressed in the plant so- 

 cieties, that the root excretions accamulating in the soil may be 

 unfavorable for the continuance of one plant society, but permit 

 another society to replace it. The vegetation of Maryland is 

 predominantly mesophytic and on the residual soils of the Pied- 

 mont Plateau has probably attained as stable a condition as one 

 is apt to find in the Atlantic coast region. Halophytic societies 

 in the salt marshes of the tidewater region and xerophytic so- 



