84 



Elementary Plant Physiology. 



8i. Presence of substances in solution in the 

 soil. — Take a few kilograms of garden soil and shake in a 

 large flask with distilled water for several minutes. After 

 standing for half an hour, filter into a large clean evaporating 

 dish, and evaporate to dryness. If a residue is obtained, it will 

 denote the presence of substances in the soil. Note the char- 

 acter of the residue. It may be of value to evaporate a similar 

 quantity of distilled or rain water in another dish, as a control 

 test. 



82. Corrosive action of plants on minerals. — Fill a 

 five-inch pot with clean sand to a depth of 8 cm. Now lay a 

 small piece of polished marble or an oyster-shell on the sand, 

 with the polished surface uppermost. Place three or four beans 

 on the shell or marble, and cover to a depth of a few centi- 

 meters with fine soil. Set the preparation where it may receive 

 proper care and temperature. Two weeks later, after the 

 beans have sprouted, and attained a height of several centi- 

 meters, take out the marble or shell, wash completely clean 

 with water, and dry. Now observe the glistening surface by 

 reflected light, and note the etching of the surface in places 

 which have been in contact with the roots. Test the acidity 

 or alkalinity of the roots of the bean, using litmus paper. Not 

 all plants are capable of corroding 

 rock or lime compounds in the 

 above manner. 



83. Water cultures. — Pro- 

 cure a number of jars with a 

 capacity of one to two liters, and ■ 

 fit them with a wooden top with 

 a slit cut from one edge to the 

 center. Germinate a number of 

 peas, beans, or the seeds of Con- 

 Fig. 57.— Wooden fitting for volvulus. Make a culture solution 



top of water-culture jar. After ^ ,, - ,, . , . 



Qgtmgr_ of the followmg substances : 



