708 



SCIENCE. 



[N. S. Vol. XII. No. 306. 



It is necessary to cite only her manufactures 

 involving high temperatures, such as the 

 porcelain industry, to appreciate the help 

 afforded by the Eeichsanstalt. The meth- 

 ods and instruments elaborated there for 

 the exact measurement of high tempera- 

 tures constitute a splendid contribution 

 toward industrial supremacy in those lines. 

 The German government sees with great 

 clearness that the Eeichsanstalt justifies the 

 expenditure made for its maintenance, not 

 by the fees received for certifications and 

 calibrations, but by the support it gives to 

 the higher industries requiring the applica- 

 tion of the greatest intelligence. In this 

 connection it should be thankfully acknowl- 

 edged that the services of this imperial es- 

 tablishment are placed at the disposal of 

 foreign institutions of learning with the 

 most generous liberality. The charges for 

 calibration are only about one-fourth the 

 expense incurred in making them, but the 

 support thus given to German makers of 

 instruments of precision, by increasing their 

 foreign orders, is deemed a suflicient return 

 for the services rendered. 



Heney S. Caehaet. 

 Univbesity of Michigan.* 



PLANT GEOGRAPHY OF NORTH AMERICA. 



I. 



THE PHYSIOGEAPHIC ECOLOGY OF NOETHEEN 



MICHIGAN. 



I. Tlie Physiographic Standpoint in Ecology. 

 — "Warming's classification of plant forma- 

 tions, doubtless the best we have, is in- 

 adequate to explain many of the facts that 

 are brought out in field study. "While 

 water is certainly the most important single 

 ecological factor, it cannot be made the 

 only standard for classification ; the differ- 

 ence between the flora of drained and un- 

 drained swamps is not a question of water 

 content, but probably of drainage ; a heath 

 and a moor have similar ecological adapta- 

 tions, but are very diverse as to water con- 



tent. A classification to be correct must 

 also be dynamic and must present the flora 

 of a district from the standpoint of its past 

 and future, thus dealing with genetic rela- 

 tionships. A classification which runs par- 

 allel with the normal physiographic changes 

 in a region meets all these needs and pre- 

 sents the flora as a unit, taking account of 

 all the interrelations. The various ecolog- 

 ical groups or plant formations are pre- 

 sented in a historical sequence, ending in a 

 normal climax or culminating type, coi-re" 

 spending to the base level of physiography, 



II. Application of the Physiographic Stand- 

 poi7it to Northern Michigan. — A. Progressive 

 Development of Plant Formations. The 

 vast majority of natural formations are de- 

 veloping toward the climax type, which for 

 Northern Michigan is a mixed forest in 

 which the hemlock, beech and sugar maple 

 dominate. At the outset the conditions 

 may be xerophytic or hydrophytic (using 

 these terms in the original sense as referring 

 to the water content of the soil) . 



1. Xerophytic to Mesophytic. In a 

 young region, xerophytic formations are 

 found commonly on hills and along exposed 

 shores. The development on the hills is 

 widely variant ; perhaps the climax condi- 

 tion is first reached on clay hills, because 

 of the ease with which water is held and 

 humus formed. Sand hills reach meso- 

 phytic conditions relatively late, because 

 they possess opposite physical characters. 

 Rock hills commonly have a slow develop- 

 ment because disintegration and soil forma- 

 tion are first necessary ; a lichen vegetation 

 first appears, then a crevice vegetation, 

 finally other stages, closing with the meso- 

 phytic forest. Rock hills of course vary 

 greatly among themselves, the development 

 being almost inconceivably slower on gran- 

 ite or quartzite than on limestone or shale. 

 Xerophytic shores are much more uniform, 

 having first an annual, then a perennial 

 vegetation, and finally the several forest 



