PLANT FORMATIONS 177 



bell glass (e.g. young plants of any xerophytio grasses, houseleeks, 

 dandelions, shepherd's purse, gorse i). 

 G. Tolerance of salt, as determined by water cultures, in one to six per 

 cent solutions of seedlings of ordinary garden annuals and seedlings 

 of such halophytes as the salt-marsh grasses {Spartina and others), 

 marsh rosemary (Statice), samphire (Salicomia), and saltwort (SaZsofa). 

 The plants which live longest with the roots immersed in a solution of 

 any given strength are the most decidedly halophytio. 



References. Kerner-Oliver, 2 ; Schimper-Fisher, 56 ; Warming-Graebner, 

 57 ; Haberlandt, 33. 



PLANT FORMATIONS; ZONATION 



159. Field study of formations.* * Visit any well-defined forma- 

 tions that are readily accessible, such as lake or pond, marsh, 

 river valley ("bottom land "), upland woods, hill or cliff side, wet 

 prairie, dry prairie, and other formations. 



A. Note what are the characteristic plants of each kind of 

 formation and, if necessary, collect specimens of these and 

 bring them to the laboratory to be named. 



B. Make a detailed study of at least one formation, noting all 

 that is possible of the physical conditions, especially of mois- 

 ture and light, the habits of life, and mutual relations of 

 the plants which compose it. For example, if the formation 

 is a wooded one make lists of : 



(1) The trees, their grouping, relative height, relative density 

 of shade, comparative number of each species, probable 

 origin (e.g. means by which seeds were planted and source 

 from which they came). 



(2) The larger shrubs. 



(3) The undershrubs. 



(4) Herbaceous plants. 



(5) Parasitic or saprophytic seed plants. 



If there is any law to account for the way in which the 

 plants of (2), (3), and (4) are unequally distributed over the 



1 Ulex. 



