330 PLANT LIFE. 



resembling, so far as outline goes, that of the grasses ; 

 whilst Yarrow, Buttercups, and Umbelliferae have finely 

 divided leaf segments which are able to compete for 

 sunlight with the numerous grass blades. Such grass- 

 lands are always difficult to keep in the same condition. 

 If at all neglected, they tend to throw back to the 

 original vegetation of the region which has generally 

 been either marsh plants, such as rushes, or forest. Each 

 plant in a grass field has a specially favourite situation 

 as regards water. Thus, Poa pratensis is said to prefer 

 a rather dry soil with subsoil water 6 to 9 feet below 

 the surface, while P. trivialis prefers subsoil water at 

 only 3 to 4 feet below it. The following table, for 

 the natural preferences of the plants concerned, 

 has been drawn up from data given by Feilberg 

 from observations in Denmark upon sand plains in 

 Skagen. 



Water at a depth of 3 inches. Rushes and Moor ; at 

 6 inches. Mosses and Cyperaceae ; at i 2 inches, normal 

 grass ; at I 5 inches Corn does well in dry summers, and 

 at 18 inches to 24 inches in wet seasons. If the water 

 is 30 inches to 40 inches below the surface, the ground 

 is useless for crops, and special dry climate plants 

 appear. 



The actual depths apply, of course, only to sandy 

 soil. In clay or other water-retaining ground, the 

 depths will be much greater. In Scotland the relative 

 succession is almost identical. Whenever the ground 

 is allowed to get too damp, mosses (the so-called 

 " fog ") make their appearance. This frequently con- 

 sists of Hylocomiuni squarrosuvi^ H. triquetrum^ species 

 of Hypnum, and other mosses or liverworts, such as 

 Lophocolea bidentata. The wetness of the soil tends to 

 choke the grass roots ; and on the moist earth, between 



