270 



Principles of Plant Culture. 



Cell structure (12). The students examine the pulp of 

 a mealy apple and of a potato, and cross- sections of a 

 young bean plant, with simple lenses of rather high mag- 

 nifying power. If a compound microscope is available, 

 many mounted objects illustrating the cell structure of 

 plants may also be shown. 



_,, ^ Absorption of water by seeds (26). For the 



exercises suggested by paragraphs 26 and 

 27, a means of weighing and of measuring the 

 volume of large seeds, as beans, with some 

 degree of accuracy is needed. The device 

 shown in Fig. 176 answers this XJurpose, and 

 one can be provided for each pair of stu- 

 dents at a moderate cost. It consists of a 

 graduated glass cylinder of 200 cubic cen- 

 timeters capacity and a test tube about 6 

 inches long. For determining the volume, 

 the cylinder is partly filled with water and 

 the height to which the water rises is noted. 

 The seeds are then dropped in and the glass 

 is shaken a little to remove the air bubbles. 

 The height of the water is again noted, 

 when the difference in the two readings in- 

 dicates the volume of the seeds in cubic 

 centimeters. For weighing, the empty test 

 tube is placed in the cylinder in the posi- 

 tion shown (Fig. 176). The height to 

 which the water rises is then noted, after 

 which the seeds are dropped into the test 

 Fig. 176. Device tubc, and the top of the cylinder is jarred 

 for weighing and gijo-htlv by tapping it with the pencil. 



determining the " » J _ J t-i » . ■ 4. j 



voimne of seeds. The height of the water is again noted, 

 when the difference in the readings indicates the weight 

 of the seeds in grammes. 



The test tube should float in the center of the cylinder, 

 as shown, and the readings should be taken with the eye 

 on a level with the surface of the water. 

 '" Each student (or pair of students) is provided with 

 the apparatus shown in Fig. 176, and with two bottles of 

 at least 100 cc. capacity, with corks. Each bottle should 



