Plate 21. — Various types of vessels used for 

 nutrient solution experiments, ranging- from large 

 tanks, 10 feet long, to small pyrex baking dishes. 

 The tanks are made of welded black sheet iron — 

 coated on the inside with non-toxic asphalt paint 

 and on the outside with asphalt paint and a coat 

 of aluminum paint. The choice of container de- 

 pends on the objective of the experiments; size of 

 plants to be grown, necessity for maintaining pur- 

 ity of culture, density of spacing of plants, kind 

 of aeration, etc. 



