THE QUADRAT METHOD IN TEACHING ECOLOGY 279 



next. These data teach greater lessons each year. The fact 

 that all the work has been done by fonner students adds interest. 

 Such a study makes the method of inference, that is the piecing 

 together the course of development of the associes and consocies 

 found in the region, much clearer and more accurate. Of 

 course such work is further supplemented by peiTiianent cjuad- 

 rats in stabilized areas, denuded quadrats, planted quadrats, 

 ecotone transects extending from shrub to prairie or woodland 

 to shrub, or across the zones of Spartina, Typha, etc., in ravines, 

 and by bisects. A series of denuded quadrats, each set a year 

 older than the preceding, gives at once the stages leading to 

 stabihzation. By means of these pennanent studies, coupled of 

 course with factor data and measurements of the plant responses 

 such as transpiration, photosynthesis, and growth in the several 

 habitats, a student is enabled to gain a maximum of results with 

 a minimum expenditure of time. 



ILLUSTRATIVE EXPERIMENTS IN RUDERAL VEGETATION 



An easy approach to the use of the quadrat method by students 

 whose floristic know^ledge is rather limited is by the study of 

 families of large ruderals such as Ambrosia trifida, Helianthus 

 annuus, Iva xayithiifolia, etc. Such work may be used to illus- 

 trate certain laws of competition in a very satisfactory manner. 

 Necessarily competition is greatest between individuals or 

 species which make similar or identical demands upon the same 

 supply at the same time. 



On April 27, 1916, the plants in three square meters, selected 

 as representative of a w^aste area, were carefully counted. Then 

 the quadrats were permanently marked. This area consisted of 

 a small level tract of very rich loam soil of alluvial origin. The 

 average number of plants per square meter was 10,500. Prac- 

 tically all were Ambrosia trifida; only a few Polygonum pennsyl- 

 vanicum and an occasional Solanum rostratum were also present. 

 At this time the plants averaged 9 cm. in height and had roots 

 about 25 cm. long. A count on June 22 gave an average of 

 only 206 plants per square meter, while on July 24 this number 

 had been reduced to 100 per unit area, all of which were rag- 



