278 PRINCIPLES OF PLANT CULTURE 



readily absorb moisture at ordinary temperatures, a few 

 kinds do not, and seeds of the latter class need to be 

 soaked cautiously, before planting, in hot water (27). 



The rate at which seeds absorb water depends 



(a) Upon the water content of the medium (27). 

 Weigh 3 samples of navy beans. Place one sample in 

 water, a second in very damp earth and the third in 

 slightly damp earth. Weigh again the next day and 

 compute the water absorbed by the three lots. 



(6) Upon the point of contact. Weigh 2 samples of 

 navy beans, placing one sample in moist soil without 

 compacting, and the second in the same kind of soil well 

 compacted about the seeds. Determine the water ab- 

 sorbed by the two samples the next day. 



(c) Upon temperature. Repeat the above with 2 sam- 

 ples of navy beans, placing one lot in a temperature of 

 80 to 90 F., and the other in 40 to 50 F. 



Other means of using the apparatus shown in Fig. 

 174 will occur to the thoughtful teacher. It may be used 

 for determining specific gravities by dividing the weight 

 by the volume. 



Germination (28) . Give an exercise in testing seeds 

 with the apparatus shown in Fig. 6. 



Moisture essential to germination (29) . Soak one lot 

 of navy beans in water until they are fully swollen and 

 another lot until they are about half swollen. Wipe the 

 beans as dry as possible, put each lot into a bottle, cork 

 the bottles, and set them in a warm room. The fully- 

 swollen beans will usually germinate promptly, while the 

 others will not. 



Oxygen essential to germination (31). Perform the 

 saucer experiment as described. 



Also place seeds of rice in two bottles, and add to 



