:;h the plant life of iiaeyland 



All of these physical features of Maryland have heen treated in de- 

 tail in previous publications of the Maryland Weather Service, and 

 in those of the Maryland Geological Survey and the United States 

 Soil and Forestry Bureaus, to the most important of which publica- 

 tions reference is made in the Bibliography at the close of the chapter. 

 Part II. deals with the Floristic Plant Geography of the state, in 

 which the three floristic zones, the Coastal, Midland and Mountain, 

 are characterised, and their principal features discussed. (See 

 Frontispiece. ) The succeeding chapters take up the Ecological Plant 

 Geography of the five Ecological Districts of the state, into which the 

 Floristic Zones have been subdivided. The Coastal Zone is sub- 

 divided into the Eastern Shore District and the Western Shore Dis- 

 trict, the portions of the Coastal Plain lying east and west of the 

 Chesapeake Bay, respectively. The Midland Zone is subdivided into 

 the Lower Midland District and the Upper Midland District, the 

 boundary between them being Parr's Ilidge. In the Mountain Zone 

 no subdivision has been made. 



CLIMATOLOGY. 



Those various elements of temperature, rainfall, humidity, etc., 

 which we designate collectively as the climate are of fundamental in- 

 fluence on the vital processes of plants. In the study of the influence 

 of each of these climatic elements, or environmental factors, on the 

 physiological processes of plants they are found to possess minimum, 

 optimum and maximum intensities. There is, for example, an 

 optimum temperature for growth in each species which may not be 

 the same as the optimum temperature for transpiration or photo- 

 synthesis in the same species. Since, however, the separate pro- 

 cesses of an individual plant operate in harmony, there is a given 

 temperature which is the physiological mean of the optimum 

 temperatures of the separate processes, which is designated the 

 ecological optimum. In the general consideration of the influence of 

 climate on the vegetation of larger areas it is necessary to confine the 

 attention to the ecological optimum. 



The climatic factors which are of the greatest importance in rela- 

 tion to the vegetation are temperature and rainfall, the first of which 

 is almost exactly uniform over areas of considerable extent, while 



