20 



PRINCIPLES OF PLANT CULTURE 



We have seen that protoplasm in its active state re- 

 quires oxygen (13). Unless seeds are so planted that a 

 certain amount of this free oxygen can reach them, they 

 cannot germinate. This probably explains why very 

 deeply planted seeds rarely germinate. Ordinary water 



contains a little 

 free oxygen, but 

 not enough to 

 enable many kinds 

 of seeds to germi- 

 nate in it, though 

 the seeds of some 

 water plants, as 

 the water lily and 

 rice, will germinate 

 in water. But 

 even these will not 

 germinate in water 

 that has been boiled 

 long enough to ex- 

 pel the oxygen, and 

 is placed under con- 

 ditions that pre- 

 vent its absorption 

 again (Fig. 5). 



We thus see that 

 seeds require three conditions before they can germinate, 

 viz., a certain amount of moisture, of warmth and of 

 oxygen. In planting seeds, we should consider all these 

 requirements. 



32. Prompt germination important. As a rule, the 

 sooner a seed germinates after it is planted, the better, 

 for it is generally in danger of being destroyed by animals 



FIG. 5. Germination and air. Rice grains 

 in water which was previously boiled to ex- 

 pel the oxygen. In the bottle at the left, 

 the water was covered with oil to prevent 

 it from absorbing oxygen again, hence the 

 seeds in it could not germinate. In the 

 bottle at the right, the water was not 

 covered with oil and so it could absorb oxy- 

 gen, permitting the seeds to germinate. 



