Januabt 18, 1907] 



SCIENCE 



103 



quent diversity of vegetation-types offer ex- 

 ceptional opportunities for this line of re- 

 search. 



Mrs. Clements's paper, which constitutes 

 another of the valuable contributions to eco- 

 logical botany that have issued from the 

 School of Botany of the University of Ne- 

 braska, should, therefore, receive a cordial wel- 

 come, the more so as it embodies the results 

 of a well-considered and carefully executed 

 plan of investigation. One is impressed at 

 first glance with the great amount of pains- 

 taking work that has been necessary to carry 

 out this plan. Not only have the details of 

 leaf anatomy been studied in about 300 species 

 of plants, most of which were represented by 

 at least two different habitat-forms, but a 

 large number of measurements were necessary 

 to obtain the normals of the more important 

 physical factors for each of a score of 

 habitats. The methods followed are those 

 outlined in Dr. F. E. Clements's ' Eesearch 

 Methods in Ecology.' The investigations were 

 carried on during the summers of 1903 and 

 1904 in the mountains and foothills around 

 Pikes Peak, Colo., with headquarters at the 

 alpine laboratory of the University of Ne- 

 braska at Minnehaha. The paper begins 

 with a survey of the most important litera- 

 ture. In a table on page 29 are presented the 

 normals of light, atmospheric humidity, tem- 

 perature (of the air, the surface of the ground 

 and the soil) and water content of the soil 

 for each of the habitats studied. The greater 

 part of the paper is devoted to brief descrip- 

 tions of the leaf anatomy of the species exam- 

 ined, both as to the normal structure and as 

 to the variations caused by change of habitat. 

 Quantitative variations were given much at- 

 tention and were carefully measured. ' En- 

 demic ' species (those occupying only one 

 habitat) are grouped according to habitat 

 under the three types of hydrophytic, meso- 

 phytic and xerophytic plants. ' Polydemic ' 

 species (those occurring in more than one 

 habitat) are also grouped as hydrophytes, 

 mesophytes and xerophytes, according to the 

 normal habitat of the species, but their classi- 

 fication according to habitat is not carried 

 further. Instead, under each species name is 



given a synopsis of the chief physical factors 

 of the normal habitat, with brief descriptions 

 of the corresponding leaf structure, followed 

 by indications of the points of difference in 

 the physical factors and leaf structure in the 

 other habitats of the species. 



A series of tables of species follow in which 

 are graphically expressed the variations from 

 the normal leaf structure that accompany de- 

 partures from the normal environment, the 

 varying factors of the latter being stated at 

 the head of the table thus: 'light unchanged, 

 water and humidity decreased.' 



In the summary are stated the most impor- 

 tant of the author's conclusions as to the effect 

 upon the anatomical structure of leaves of 

 each of the physical factors studied, attention 

 being called to the points of agreement or of 

 disaccord with the results of Heinricher, Du- 

 four, Stahl and other well-known investiga- 

 tors. In future researches the writer believes 

 that the phases of the subject which should 

 receive especial attention are : " (1) the hered- 

 itary structure, which should include consid- 

 erations of size, shape and position of leaf, 

 as well as histology and modifications, such 

 as hairs, stomata, mucilage cells and the like; 

 (2) exact records of the physical factors of 

 the habitat of the species for the day and for 

 the growing season; (3) the physiological 

 processes of the leaf; (4) the interrelation 

 and correlation of the preceding data." 



The paper is illustrated by nine excellent 

 plates, showing the habitat variations of many 

 of the species described. 



To say that Mrs. Clements has published 

 one of the most important papers dealing with 

 this phase of American ecological botany is 

 to render no more than justice to her achieve- 

 ment. An especially commendable feature of 

 her work is the great volume of careful ob- 

 servations that serve as a basis for what gen- 

 eralizations are made. So high a ratio of 

 fact to theory does not always characterize 

 this branch of botanical literature. A good 

 service has been rendered to American stu- 

 dents of plant ecology by pointing out a field 

 for future research which can not fail to be 

 fruitful of results. 



Thomas H. Kearney 



