78 



BOTANY 



the proper stimuli are applied to it, start in its growth into a 

 new plant. Let us see what these stimuli are. 



Effect of Water on Dry Seeds. — Weigh ten dry navy beans; leave them in 

 water over night; reweigh. How much have they increased in weight? 

 We have already found that water gets into the seed through the micropyle. 

 It can be proved that it gets in through the seed coat as well. If you cover 

 five seeds entirely with paraffin, and in five others cover the hilum, micropyle, 

 and half of the remainder of the coat, a difference in weight and size will 

 be apparent the next morning. 



Expansive Force of Germinating Seeds. — The expansive force of germinat- 

 ing seeds is considerable. You have noticed that the bean is considerably 

 larger after soaking. 



Fill a small bottle almost full of dry seeds (beans or peas) , then fill the 

 space left with water; wire in the cork tightly. Leave the bottle overnight 



and note the results next morn- 

 ing. Would this force be of use 

 in getting a start under the soil ? 

 Have you noticed that the soil is 

 lifted in the garden by the rows 

 of germinating peas and beans just 

 before they come up ? Is this due 

 entirely to the expansive force of 

 seeds ? Watch future experiments 

 before you attempt a definite an- 

 swer. 



Will a Dry Seed germinate? — 

 Place a layer of moist blotting 

 paper or sawdust in bottom of 

 each of three cups or three tin 

 cans. Soak fifteen navy beans 

 overnight. Place five in each 

 dish. Water one dish so as to 

 cover the seeds ; water the second 

 so as to keep sawdust rather 

 moist; let the third remain unwatered. Cover the cups with loose-fitting 

 covers. Make daily observations of the number germinating, and the con- 

 dition of each for at least ten days. Put the results in tabular form. What 

 amount of water is most favorable for germination of the navy bean ? * 



Water a Factor in Germination. — A dry seed will not germinate. 

 Water is absolutely necessary to start the forces at work toward growth. 

 But it is sometimes difficult to determine the amount of water 

 that is most favorable to germination. Some seeds require a great 

 deal of water, others require very little. 



Will a Seed grow without Air? — We have already seen that in 

 the germinating corn plant the starch stored in the endosperm 

 was changed to grape sugar by the action of a digestive ferment 

 called diastase. This sugar was then used by the plant as food. 



* See Huiiter and Valentine, Manual, page 222. 



The expansive force of germinating seeds. The 

 flower pot to the left was filled with dry 

 beans, a block of wood wired on, and the 

 whole apparatus placed in a pail of water 

 over night. The right-hand figure shows 

 the result. 



