282 



Principles of Plant Culture. 



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Cell structure (12). The students examine the pulp 

 of a mealy apple and of a potato, and eross-sections_ of 

 a young bean plant, with simple lenses of rather high 

 magnifying power. If a compound microscope is avail- 

 able, many mounted objects illustrating the cell struc- 

 ture of plants may also be shown. 



Absorption of water hy 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. 174 

 answers this purpose, and one can be 

 provided for each pair of students at a 

 moderate cost. It consists of a graduated 

 glass cylinder of 200 cubic centimeters 

 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 re- 

 move the air bubbles. The height of the 

 water is again noted, when the difference 

 in the two readings indicates the volume 

 of the seeds in cubic centimeters. For 

 weighing the empty test tube is placed in 

 the cylinder in the position shown (Fig. 

 Fig. 173. Device l'^^). The height to which the water 

 for weighing and riscs is then noted, after which the seeds 

 voi*u™'°f°^seeds^ ^I'B dropped into the test tube, and the 

 top of the cylinder is jarred slightly by 

 tapping it with a pencil. The height of the water is 

 again noted, when the difference in the readings indi- 

 cates the weight of the seeds in grammes. 



The test tube should float in the center of the cylin- 

 der, 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. 173, and with two bottles 



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