830 



SCIENCE 



[N. S. Vol. XXVII. No. 



does the first-mentioned Quercus alba forma- 

 tion. 



E. Talus slopes, at the foot of which are 

 the flood plains of the modern larger rivers 

 and tributaries; soil largely derived from 

 other habitats by landslides, thus usually deep 

 and more or less mixed with rock fragments. 

 The upper part of this habitat, and often the 

 newer or more unstable portions down to the 

 base, is chiefly characterized by what may be 

 termed the Samhucus puhens talus thicket 

 formation; facies, the red-berried elder. In 

 the lower portion of the habitat and in the 

 more stable portions this formation is dis- 

 placed, often plainly succeeded, by the nest 

 forest formation to be characterized. 



F. The present flood plain of the modern 

 rivers and larger tributaries; altitude of about 

 750-7Y5 feet A.T.; soil a deep, sandy, moist, 

 fertile alluvium. So far as can now be de- 

 termined this habitat was formerly occupied 

 by a climax Acer-Ulmus forest formation; 

 facies — Acer saccharinum, Acer rubrum, Ul- 

 mus americana. This formation, as indicated 

 by a few isolated remnants, was characterized 

 by a greater number of tree species than any 

 of the other forests of the region. Many large 

 sycamores in this forest are to be regarded as 

 relicts of the next fonnation. 



G. The river banks and low islands sub- 

 ject to inundation during times of floods, 

 especially in winter and spring. This habitat 

 is characterized by the Platanus-Salix river- 

 bank forest formation; facies — Plaianus occi- 

 dentalis L., and Salix nigra Harsh. With the 

 meandering of the stream the habitat often is 

 occupied by the Acer-Ulmus forest formation 

 but the sycamores remain as relicts even after 

 the succeeding forest has reached maturity. 



H. The sand bars in the rivers, ordinarily 

 covered by shallow water. This habitat is pre- 

 eminently characterized by the Dianthera 

 americana sand-bar formation; facies, Dianr 

 thera americana L. With the upbuilding of 

 the bar this formation is succeeded by the 

 Platanus-Salix river-bank formation. 



Besides the above-mentioned formations 

 there are several less conspicuous formations 

 and no mention has been made of various 

 successional f onnations, especially those of sec- 



ondary successions incidental to the march of 

 civilization, the purpose of this note being 

 merely to designate the more important plant 

 formations and to point out their correlation 

 with certain conspicuous habitat-structures 

 evolved in the physiographic development of 

 the region. 



Otto E. Jennings 

 Caknegie Museum 



THE "permanent PHASE " 



EoR some time it has been genert^lly ad- 

 mitted that all substances are capable of exist- 

 ing in the three phases, solid, liquid, vapor, 

 and some substances, as sulphur, in four 

 phases. We believe that all substances are 

 capable of existing in four phases, and some 

 in more. 



To show this notion, we will use the com- 

 mon text -book phase-diagram for water shown 

 in Fig. 1, in which, for the sake of clearness. 



Fig. 1 



the curves have been drawn as straight lines, 

 and only the substance in a stable condition 

 is considered. It will at once be seen that 

 OA is the curve of vapor pressure that sepa- 

 rates the region of liquid from the region of 

 vapor. However, there is a limiting pressure 

 beyond which the vapor pressure of the liquid 

 can not rise, and therefore at the value of 

 critical temperature and critical pressure A 

 the curve OA abruptly ceases. It is com- 

 monly admitted that " for temperatures and 

 pressures beyond A there is no distinction 



