June 14, 1907] 



SCIENCE 



939 



Michigan. The ridges are separated by the 

 low level prairie land which makes up the 

 Chicago Plain. 



The formation of the dunes along the pres- 

 ent shore of the head of Lake Michigan was 

 considered, and also the changes in the flora 

 that may be noted as one passes from the 

 naked shifting dunes and extremely xerophytic 

 conditions of those recently fixed, to the dunes 

 farthest inland where mesophytic conditions 

 prevail. Certain grasses, species of Calama- 

 grostis, Andropogon, Ammophila, Elymus, do 

 much to bind the dunes. The first trees to 

 appear are the cottonwood and certain willows 

 which are also of value in fixing the dunes. 

 The scrub-oak and black-oak soon appear and 

 are followed by the bur-oak, the white-oak, 

 and the red-oak. Pinus Banksiana is followed 

 by the white pine; the pig-nut hickory is suc- 

 ceeded by the shag-bark; other trees, such as 

 the basswood, ash, cherry and black walnut, 

 come in, and on the most mesophytic slopes 

 of the oldest dunes and beaches one finds the 

 Bugar maple and, more rarely, the beech, hem- 

 lock, and southern tulip-tree. Corresponding 

 changes in the shrubby and herbaceous vege- 

 tation occur, and at Stevensville and Porter, 

 one may pass, in a short time, from extreme 

 desert conditions through successive stages of 

 the open forest of low trees and shrubs to the 

 oak-hickory type and finally to the beech- 

 maple-hemlock combination, which indicates 

 the culmination of the forest in this region. 



The usual ecological factors, heat, light, 

 water, soil, wind, and direction of slope all 

 have their influence in the floral distribution. 

 Conditions in the dunes are extreme. Thus, 

 for example, the trailing-arbutus and the bear- 

 berry, both northern types, may appear on the 

 north-facing slope of a dune, while just over 

 the crest, on the south-facing slope, the cactus 

 may flourish. 



Emphasis was laid on the fact that species 

 vary with environment, often losing more or 

 less of their xerophytic adaptations under 

 mesophytic conditions; that a plant-society is 

 only a stage in the development of a region; 

 that the apparent tendency is for all to ap- 

 proach the mesophytic condition. 



The paper was discussed by Dr. Grout and 

 Dr. Eydberg. 



Some Belaiions ieiween Habitat and Struc- 

 ture in Mosses: Dr. A. J. Grout. 

 Xerophytic mosses apparently tend to de- 

 velop short, thick-walled cells, often with 

 papillae over the lumen. Nearly aU mosses 

 with papillae over the lumen of the cell are 

 xerophytic, or belong in groups that are 

 largely xerophytic. Presumably the papillse 

 tend to retard transpiration. 



Pleurocarpous mosses growing on trees tend 

 to develop short thick-walled cells, especially 

 at the basal angles, and a similarity of leaf 

 structure in tree-growing mosses due to this 

 fact has produced much of the confusion and 

 uncertainty in classifying such mosses, e. g., 

 Alsia, Dendroalsia, Bestia, Groutia and their 

 relatives. 



Tree-growing mosses also tend to develop 

 erect capsules, and the correlated imperfect 

 peristomes. To some extent this seems to 

 apply to other xerophytic mosses. 



Aquatic or subaquatic pleurocarpous mosses 

 have an apparent tendency to develop enlarged 

 and inflated alar cells. 



Cleistocarpous and gymnostomous mosses 

 appear, for the most part, to be mosses of 

 various relationships adapted to damp soil, not 

 closely covered with other vegetation, and best 

 suited to support a rather short-lived annual 

 moss. 



The speaker recognized numerous excep- 

 tions to the above relationships, if stated as 

 general principles, but, stated as tendencies, 

 he believes they are worthy of serious con- 

 sideration by the systematist, the morpholo- 

 gist, and the ecologist. 

 A brief discussion followed. 



C. Stuart Gager, 

 Secretary 



DISCUSSION AND CORRESPONDENCE 



ELIMINATION OR FIRST SPECIES 



Having followed the discussion of the pro- 

 posed new rules of zoological nomenclature in 

 the pages of Science, I feel that I voice 

 the opinion of many zoologists when I say ' a 

 plague o' both your houses.' For thirty years 



