154 PLANT PHYSIOLOGY AND ECOLOGY 



of which is raised from time to time so that the leaves are kept floating. 

 These two series are handled most conveniently if the plants are grown 

 in a deep tub or a half-barrel. The last series should be grown in a large 

 barrel or in a deep box, one side of which is replaced by glass. Six 

 inches of soil are placed in the bottom and a faucet is inserted in the 

 side just above the soil. This is to aid in the aeration of the water 

 from time to time, as well as to make it possible to draw it off readily 

 in case it becomes stagnant. The water level is kept just above the 

 leaves as they stretch up. In case the leaves begin to turn yellow, they 

 are allowed to float on the surface until they regain the normal color. 



All the series should be grown in the same house where heat, light, 

 humidity, etc., are the same. In this event all the modifications ob- 

 tained can be referred with certainty to water content as the cause. 

 In the three series, mud, floating, and submerged, the soil is saturated 

 and it is unnecessary to measure the water content. The latter should 

 be determined several times during the course of the experiment for the 

 three series in soil. The growth and the behavior of the jjlants of the 

 various series should be carefully followed and compared throughout 

 the experiment. In connection with growth, it is sometimes desirable 

 to compare the soil temperatures with those of the water. When the 

 instrument is accessible, a water photometer should be used to deter- 

 mine the light intensity for submerged leaves, and for the under side of 

 floating ones. 



As the plants come into full flower, an individual from each series 

 should be carefully sketched, or photographed, to a fixed scale showing 

 the branching of roots and stem, leaf and flower production, etc. A 

 typical leaf should be drawn in like manner, and its area and thickness 

 carefully determined. The relative water loss should be determined by 

 placing a leaf from each series in a vial of water in the manner already 

 employed in a previous experiment. If the number of leaves on each 

 plant is counted, this will make it possible to approximate the evapo- 

 ration for the whole plant. Careful counts of stomata should be made 

 for both surfaces of a representative leaf of each series, the actual 

 transpiring surfaces, i.e., the air spaces, estimated, and a table of 

 comparisons made. Finally, microtome sections should be made of 

 similar leaves and a segment of each sketched in the proper sequence 

 to show differences of thickness, structure, etc. 



173. Types of plant body. The plant regularly bears the 

 impress of its habitat in the form or structure of some or all of 

 its organs. This impress is usually recognizable at a glance, and 

 can be referred at once to water or light stimuli. Since it is the 

 product of the present habitat, the plant which bears it is called 



