THE AMERICAN BOTANIST 35 



abound; in fact this has been so thoroughly impressed upon 

 even the popular mind that dry and sterile regions are usually 

 called heaths. Typical heath plants in the Northern States 

 are the kalmias, wintergreens, huckleberries, blue-berries, deer 

 berries, andromedas, arbutus an'd bear-berry. In the bogs of 

 such regions we find another set of heaths that may still be 

 said to be drouth plants though their roots are immersed in 

 water. This is due to the fact they find it difificult to absorb 

 moisture from the bog water. Thus while their relatives on 

 the sand hills are in a physically dry soil they are little better 

 off for their habitat is physiologically dry. Some of these are 

 the leather-leaf, marsh rosemary, cranberry, snow-berry, and 

 some of the huckleberries and laurels. It is not unusual to 

 find considerable stretches of both sand and bog in which few 

 things grow except heathworts. 



Another distinction made by the soil is due to the absence 

 of certain minerals necessary tc plants. Sandy regions are us- 

 ually lacking in nitrogen compounds and only such plants can 

 thrive in them as have special means of obtaining the essential 

 nitrogen. In the moist places we find the pitcher-plants, sun- 

 dews, butter-worts and bladder-worts setting their seductive 

 traps for insects, and on the sand hills are a multitude of 

 legumes which have gone into partnership with bacteria that 

 are able to obtain nitrogen from the air. These latter are 

 among the handsomest plants of the sand-barrens and include 

 the lupines, baptisias, tephrosias, partridge-peas, vetches, and 

 the like. 



Sand-barren plants, like xerophytes in general, have 

 numerous ways of retaining moisture, once it is in the plant. 

 The majority spread the minimum leaf surface to the air, and 

 the cactus goes altogether without leaves, such starch as it 

 needs being made by its thick stems. A great number of plants 

 are covered with hairs which very effectually retard evapora- 



