29O ECOLOGY. 



Studies in the Relation of Plants to Soil. 



Observations can be made on the plants occurring on differ- 

 ent kinds of soil, as sandy, clay, loam, rocky soil, poor or 

 rich soil, in waste places, uncared parts of fields or gardens, 

 etc. 



One very important condition of the soil is its varying 

 physical condition of texture, and the presence of 

 various chemical substances, which influence greatly the 

 character of the vegetation; but this subject could not 

 well form one for study by young students, since a 

 knowledge of the constituents of the soil would be 

 necessary. 

 Warming divides plants into four classes: 



1. Mesophytes, those plants which occupy a middle posi- 



tion with reference to the water-supply. 



2. Hydrophytes, those plants which grow in damp or wet 



situations. 



3. Xerophytes, those plants which grow in dry situa- 



tions. 



4. Halophytes, those plants which grow in soil or water 



which contains an excess of certain salts. 

 Some soils contain such an abundance of certain salts that only 

 certain plants grow there. These plants are known as halo- 

 phytes (salt loving). The salt lands in the great Salt Lake 

 basin, the alkaline lands of California, Nebraska, and Dakota 

 may be cited as examples. Certain families of plants, like the 

 goose-foots, are peculiarly adapted to growing in such soil, 

 though there are plants from a number of families which are 

 found in such situations. The great amount of salt in the soil 

 renders the absorption of water difficult by the plant, so these 

 plants are provided with means for checking transpiration, or 

 they would wilt. In this respect the halophytes resemble the 

 xerophytes, and the structures for checking rapid transpiration 

 are similar. The plants growing in the salt water are also 

 halophytes, and those which have parts that are constantly out 



