GERMINATION AND GROWTH 



35 



favorable to germination are present. Before releasing, they should be 

 well shaken under the mercury to free them from air bubbles, and if the 

 coats are loose fitting so that they can be removed without injury to the 

 parts inclosed in them, they should be slipped off in order to get rid of any 

 imprisoned air they may contain. Additional moisture may be supplied, 

 if necessary, by injecting, by means of a medicine dropper inserted under 

 the mouth of the tube, a drop or two of water that has been previously 

 boiled. Keep in a warm, even temperature, under conditions favorable 

 to germination, and compare the behavior of the seeds with those placed 

 in the different vessels in Exp. 26. 



If appliances for this experiment are lacking, a rough approximation 

 can be made by using the seeds of aquatic plants, such as the lotus, water 

 lily, and the so-called Chinese sacred bean, sold in the variety stores, 

 which we know are capable of germinating in the limited amount of air 

 contained in ordinary soil water. Place an equal number of such seeds, 

 of about the same size and weight, on a bedding of common garden soil 

 in two glass tumblers. Fill one vessel a Uttle over half full of ordinary 

 soil water and the other to the same height with 

 water from which the air has been expelled by boil- 

 ing. Pour over the liquid a film of sweet oil or castor 

 oil, to prevent the access of air, leaving the surface of 

 the water in the other vessel exposed. In which do 

 the seeds come up most freely ? 



Some seeds, especially those rich in proteins, as 

 peas and beans, will germinate in a vacuum, because 

 oxygen is supplied for a time by the chemical decom- 

 position of substances in their tissues which contain it, 

 but when these are exhausted, respiration ceases and 

 death ensues. 



Experiment 28. Does the depth at which seeds 



ARE PLANTED AFFECT THEIR GERMINATION ? — Plant a 



number of peas or grains of corn at different depths 

 in a wide-mouthed glass jar filled with moist sand, as 

 shown in Fig. 47, the lowest ones at the bottom, the 

 top ones barely covered. Try different kinds of seed 

 and grain, — radish, squash, cotton, or wheat, — and 

 watch them make their way to the surface. Do you 

 notice any difference in this respect between large 

 seed and small ones ? Between those with thick coty- 

 ledons and thin ones ? At what depth do you find, 

 from your recorded observations, that seed germinate 

 best?" 



Fig. 47. — To find 

 out the proper depth 

 at which to plant 



