176 The Plant World. 



ing in definite layers of the peat substratum are the leading fac- 

 tors in producing physiological aridity, and it also appears that 

 this bacterial flora plays an important part not only in the forma- 

 tion of toxins, but also in the slow and partial decay of bog and 

 swamp plants; and this retardation of growth appears plainly 

 to be caused, not by physical or chemical conditions, but through 

 the direct activity of the bacterial flora upon the peat sub- 

 stratum. 



The extended study of physiological factors which has been 

 made by the author leads to the conclusion that, contrary to ac- 

 cepted views, low substratum temperatures play no part in bog 

 structure or bog development. It appears also that the evapor- 

 ating power of the air in bogs is not an important limiting factor 

 in controlling bog vegetation, or determining the character of 

 it. There is, on the contrary, a vapor blanket over the surface 

 of bogs which conserves the moisture that would otherwise be 

 lost by evaporation. Hence the weight of evidence is again de- 

 cidedly in favor of the conclusion that the real determining 

 factor in the bog habitat is the ratio of the possible rate of water 

 absorption to the rate of transpiration, and that the toxicity 

 of the bog habitat has a primary role in bringing about bog con- 

 ditions. 



The first part of Professor Edward Lee Greene's "Land- 

 marks of Botanical History" has appeared as part of Volume 54 

 of the Smithsonian Miscellaneous Collections. Its sub-title, 

 "A Study of Certain Epochs in the Development of the Sci- 

 ence of Botany," indicates the author's purpose, which, as 

 more fully set forth in the preface, is "to evade the responsibil- 

 ities of the consecutive historian, thus leaving him free to bring 

 into clearer light the lives and teachings of those and those only 

 among botanists of the past whose names are more familiar." 



The spirit of the undertaking is further shown by the words 

 "The historian who is both conscientious and discreet will give 

 small heed to popular opinion about any particular man or epoch. 

 Neither the adulation of the multitude is of any profound im- 

 port, nor its voiceless indiff"erence. Its outspoken opposition or 

 denunciation may even be the highest praise." Needless to 

 say that a work conceived and executed from this standpoint 



