LABORATORY AND FIELD WORK 267 



wind velocity, a psychrometer for measuring relative humidity 

 (Fig. 116), a stop-watch, a soil thermoiueter, and a soil can for taking 

 a sam])le for determination of soil-water content. Each grouj) 

 worked upon a time-schedule ])revi()usly agreed upon so that eac-h 

 kind of measurement was made simultaneously in all five habitats. 

 The groups then exchanged data and were asked to explain the dif- 

 ferences in vegetation in the five habitats on the basis of the differ- 

 ences in physical factors. The second method used was similar to 

 the first except that instead of working on a time-schedule each group 

 of students was given a set of instruments and told to devise methods 

 of making a thorough investigation of one of the five habitats. 

 While this method gave less accurate data than the former it had the 

 advantage of placing the students more upon their own responsi- 

 bilities with fewer specific directions to follow. 



Suggested Problems 



1 . To learn to use common instruments for making measurements 

 of the physical factors of the environment. 



2. To make a thorough investigation of the physical environment 

 of a single plant. 



3. To make a comparison of five habitats as to the physical factors 

 of the environment. 



4. To discover reasons for differences in vegetation in five habitats. 



5. To compare the evaporation rates in five habitats. (Porous 

 clay-cup atmometers would be useful for this) (Fig. 117). 



Quadrat Methods.— A quadrat is a square area used for making 

 studies of vegetation (Fig. 118). A quadrat may be of any con- 

 venient size such as 1 meter square or 10 feet square or 100 feet 

 square. Quadrats are used in various ways and are designated 

 accordingly. A list quadrat is one in which the plants are counted 

 and a list is made of the species with the number of each. A chart 

 quadrat is one which is charted on paper and the position of each 

 plant in the quadrat is shown. A denuded quadrat is one from which 

 the vegetation has been removed, while a permanent quadrat is one 

 that is staked out so that observations may be made on it from year 

 to year. Sometimes in studying vegetation a transect is found to 

 be more useful than quadrats. A transect is a line drawn through a 

 plant community and usually the plants along one side or along both 

 sides of the line are listed. 



