204 THE XA TU RE-STUD Y RE VIE IV [3 : 7 _ OC t., , 9 o 7 



which the hydrogen is escaping, removing the card as soon as the 

 bottom of the chimney is below the surface of water. While in 

 this position the hydrogen will rise and displace the water in 

 the chimney. See Figure 2. When the water has been 

 displaced, place the card under the bottom of chimney so that air 

 cannot enter and mix with the hydrogen, and transfer the chim- 

 ney to a shallow dish of water. Place beside the chimney another 

 chimney of seeds arranged with moss as in previous experiments. 

 The seeds will not sprout in the hydrogen'if you succeed in exclud- 

 ing air. 



Application of this lesson. It is not commonly realized that 

 seeds require air as well as water and heat to sprout, yet 

 such is the truth taught by this experiment. The hydrogen 

 has no effect on the seeds, but is vised as a means of keeping the 

 air from them without which they cannot sprout. It is known 

 that the oxygen of the air enters the soaked seeds and starts the 

 processes of growth. Perhaps on the whole it is not wise to 

 enter into a discussion of the part played by oxygen in the sprout- 

 ing of seeds; for aside from the technical nature of the question, 

 there is considerable uncertainty about certain steps of the pro- 

 cess. The fact that air is absolutely necessary for seed sprouting 

 is so simple a truth and at the same time so important for one to 

 appreciate who raises plants that it is well worth the trouble of 

 presenting as a lesson. It is not probable that seeds often fail to 

 sprout for lack of air, for ordinary soil is well supplied with a 

 "soil atmosphere;" besides the processes by which the soil is pre- 

 pared for planting introduces large quantities of new air into the 

 soil. When the soil is soggy, or covered by pools of water, air 

 may be excluded sufficiently to prevent sprouting. 



Sprouting seeds are influenced by gravity. Prepare two chim- 

 neys as described in the first experiments. As soon as the seeds 

 begin to sprout see if you can cause the eaulicle to grow up and 

 the plumule down by putting one of the chimneys in different 

 positions. The undisturbed chimney acts as a control with 

 which you can compare the growth of the plantlets in the dis- 

 turbed chimney. 



Application of this lesson. Our inability to confuse the eaulicle 

 and plumule in direction of growth is regarded as one of the most 

 difficult activities of plant life to understand. The eaulicle 

 whose function is to secure food from the soil persists in growing 



