O EXPERIMENTAL PLANT PHYSIOLOGY. 



Bemark 1. — To exclude light from the roots and prevent the growth of 

 Algae in the culture cylinder it should be fitted with a jacket of pasteboard 

 or blackened paper. This may be still more effectively accomplished if the 

 jar is sunk its entire depth in the soil of a large fiower-pot or box. If the 

 soil is watered occasionally, a temperature more nearly suitable for the 

 roots will be obtained. 



Semark 2. — Calcium phosphate is only slightly soluble in water, and in 

 consequence it forms a sediment on the bottom of the jar which decreases 

 as that in solution is used. 



Remark 3. — The sodium chloride used in the second solution is not of 

 •direct use to the plant, but serves to keep the solution alkaline. 



Remark 4. — Analysis and agricultural practice show that plants of differ- 

 ent species and genera grown in the same soil contain the elements in dif- 

 ferent proportions ; consequently a solution suitable for all plants cannot 

 be made. Instead of the salts given above, others which contain the ele- 

 ments in soluble form may be used. The degree of concentration must be 

 kept within the prescribed limit, however. 



3. Distilled Water as a Nutritive Fluid. — A plant will grow 

 for a time in distilled water, but when the food stored in the 

 seed is consumed it perishes. 



EXPERIMENT 2. 



DISTILLED WATER AS A NUTRITIVE FLUID. 



Grow two seedlings as nearly alike as possible, one in distilled 

 water and the other in a nutritive solution as in Experiment i. 

 Note difference in lo and 14 days. 



4. The Influence of Iron. — The plant can form green color- 

 ing matter {chlorophyll^ only when supplied with iron. If 

 this is withheld, the plant dies after it has used the iron stored 

 in the seed. The presence of chlorophyll is necessary for the 

 formation of food from the carbon dioxide of the air. (§ 29.) 



EXPERIMENT 3. 



IRON-FREE NUTRITIVE SOLUTION. 



Grow two plants in an iron-free nutritive solution. The first 

 leaves are green and the later ones pale yellow (chlorotic). 



EXPERIMENT 4. 



ADDITION OF IRON TO A CHLOROTIC PLANT. 



Pour a few drops of iron solution into the culture jar of a chlo- 

 rotic plant obtained by Experiment 3. The leaves soon become 

 green. With a small brush moisten portions of a leaf of another 



