How Seedlings Get Established 



15 



Seeds will not absorb enough water from moist air to 

 make them germinate. They must be in contact with 

 a substance covered with a film of water. 



24a. The Swelling of Seeds. Place some common beans in a 

 glass of water, and observe every few minutes. Where does the 

 seed coat wrinkle first? 



24b. Rate of Absorption Affected by the 

 Amount of Water Present. Place a dozen 

 seeds in - glass of 

 water, a second dozen 

 in wet sand, and a 

 third dozen in slightly 

 damp sand. Examine 

 every day, and judge 

 the amount of water 

 absorbed, by the in- 

 creased size and weight 

 of the seeds. 



24c. Rate of Ab- 

 sorption Affected by the 

 Number of Points of 

 Contact. Take two lots 

 of seeds, corn for ex- 

 ample, and place each 

 lot in a tumbler or 

 other vessel with the 

 same amount of moist 

 sawdust In one, 

 sprinkle a layer of 



Fig. 14. A, a young root of the pea 

 marked with fine lines of water- 

 proof ink into 13 spaces. B, the 

 same root, 24 hours later, showing 

 elongation only in terminal 5 



B 



spaces. The rate of growth is 



greatest in the second and third 



spaces and slow in the first, fourth 



and fifth. Magnified 2 diam. C, tip 



of root greatly magnified and shown 



in section . w, root-cap; i, younger part of 



cap; z, dead cells separating from cap; s, 



growing point; p, central cylinder. 



sawdust, and then a layer of seeds, then another layer of each, 

 taking care that in one the sawdust is not pressed down, but kept 

 very loose. Prepare the second vessel just as above, but press the 

 sawdust firmly around the seeds. This increases the number of 

 points of contact between the sawdust and the seeds. Cover, to 

 prevent drying out, and examine the seeds at the end of every 

 twelve hours. Does pressing the sawdust about the seeds make 

 them swell more quickly? 



24d. Prompt Absorption Hastens Germination. Sow some peas in 

 a gardener's flat, filled with very loose sawdust. Press the sawdust 



