40 



is in many cases satis factoiy, especially if the associations are small 

 in area or the component plants low in stature so that a comprehen- 

 sive view of them may be taken. In other cases, simple lists of 

 species, taken in each area of the association, may be compared, and 

 their similarity is a good index. For more accurate work, the quad- 

 rat method proposed by Clements (1903: 161-170) may be employed. 

 It pfives excellent results but demands much time and labor. In areas 

 of closed vegetation it seems to have its chief value in expressing, 

 rather than determining, the structure of the association. A modifi- 

 cation of the quadrat method has been tried with success in this work. 

 It consists in listing, in the approximate order of the space occupied 

 by each (not the number of individuals), the species on an imaginary 

 quadrat of about four square meters situated directly in front of the 

 observer. Stepping forward two paces brings another quadrat to 

 view, and a series of ten or twenty, extending in a continuous strip 

 or scattered throughout the association, may be listed in a short time. 

 The size of the quadrat used is chosen to suit the character of the 

 vegetation ; two meters square seems adequate in the study of prairie 

 associations. In a forest a cjuadrat of that size could be used only for 

 the herbaceous vegetation, and one ten meters square would be neces- 

 sary to show the nature of the forest cover. Quadrats of such size 

 are unwieldy, and in practice it has been found that results are more 

 easily obtained by counting every tree within five meters of the ob- 

 server as he walks through the forest. A new list may be made for 

 each hundred meters or for any area with distinct environment. 



In in\'estigating the tension zone between associations the tran- 

 sect method (Clements, ipoj: 176-179) may be used, but is subject 

 to the same limitation as the quadrat method. Good results may b^ 

 conveniently obtained by walking back and forth repeatedly from one 

 association to the other, listing the species in the order of their ap- 

 pearance. 



Carefully conducted studies, as indicated above, show that the 

 dominant species are unifonnly distributed over the whole area of 

 the association or consocies, and that the floral discrepancies are 

 caused by a number of comparatively rare species represented usually 

 by a small number of individuals. The weakness of the whole method 

 lies in the fact that, in a mere list, a rare species, possibly a single in- 

 dividual, is given as much weight as a common one. Actual counts 

 of the individuals of each are difiicult to make and may g^ive mis- 

 leading results. If each species could be correlated with the pro- 

 portion of the area which it occupies, it would be demonstrated that 

 most parts of an association are highly similar in structure, and the 



