BOG XEROPHYTES AND ACID SOILS. 129 



the products of the decay of Nymphcea rhizomes are injurious to 

 Tradescantia cuttings and to tomato, alfalfa, and corn, even in very 

 dilute solutions, as Sherff had shown earUer. Similar results for 

 Tradescantia were obtained from the decay of potatoes and turnips, 

 and of the rhizomes of Castalia odorata and Typha latifolia. 



Rigg (1916) has summarized the data collected by Cox (1910) 

 with reference to temperature and frost in cranberry bogs in Wis- 

 consin and has reached the following conclusions : The temperatures 

 in both soil and air are less favorable in the bog than on adjacent 

 hard land. In so far as a difference of temperature between air and 

 soil is concerned, conditions in the bog are m.uch less favorable than 

 on land, frost sometimes remaining in the soil as late as the first of 

 July. With respect to relative humidity and wind velocity, the con- 

 ditions were less favorable to transpiration than on the neighboring 

 land. Rigg, Trumbull, and Lincoln (1916) have studied the osmotic 

 pressure of water from sphagnum bogs of the Puget Sound region 

 and Alaska, and they confirm the conclusions of Livingston and 

 Fitting that it is not a factor in the toxicity of bog-water or of the 

 very dilute solutions arising from the decay of Ny?nphoea rhizomes. 



In a related paper (1916'), it is suggested that low osmotic pres- 

 sure of bog-water indicates that the material in solution in it is 

 probably in a colloidal state. The data presented are regarded as 

 confirming this view and warranting the suggestion that this col- 

 loidal matter is a large factor in the toxicity of the water. 



Rigg (1916'*) has made a comprehensive summary of the theories 

 advanced to explain bog xerophytes, and indicates that part of the 

 discrepancy in opinion is due to various definitions of bog-plants. 

 While this is true in some degree, it seems unavoidable that the 

 views of Volkens, Warming, Schwendener, Kihlmann, Goebel, Sten- 

 strom, Schimper, and others must be examined in the light of the 

 species that they regarded as bog xerophytes, which are much more 

 numerous than those recognized by Rigg. 



Clements (1916 : 90) has concluded that most of the xeroid species 

 of wet places are not xerophytic at all, but that a restricted group 

 characteristic of peat-bogs and heath-moors are actual xerophytes. 

 No final decision with respect to these was regarded as possible, 

 however, until their water requirements are studied experimentally 

 and their transpiration response known. The conclusion was reached 

 that lack of oxygen is the primary factor in bogs, and the acid a con- 

 sequence or concomitant. This view was later amplified (1920: 85), 

 and the presence of acids and bog toxins was attributed to the 

 direct activity of the roots and the bog flora under conditions of 

 deficient aeration. 



Bergman (1920 : 13) has observed that growth is reduced in plants 

 with roots submerged in Sphagnum as compared with peat, and 

 ascribes this to the greater lack of oxygen in the former. When 



