146 ORGANS OF VEGETATION 



seed. Besides moisture the young plant must have plenty of air. 



If we plant wheat in one vessel and cover it with an inch or more 



of water, and place 

 on the right of it 

 another dish con- 

 taining j ust enough 

 water barely to 

 cover the wheat, 



Seed tester. 



we find in two or 



three days that the seed in the right-hand vessel which have 

 access to the air will germinate, while those in the left-hand dish 

 will not. 



This experiment shows that ordinary plants must have air 

 and that their seed must also have air before they will germinate. 

 For the same reason, seed germinate slowly, if at all, in closely 

 packed clayey soil, while, on the other hand, they germinate 

 rapidly in loose soil because the air has access to them. We find 

 that temperature also plays an important part in the process of 

 germination if we plant a few grains of corn, a few beans, and a 

 few clover seed in the same kind of soil in four different tumblers 

 and treat them as follows: Set one tumbler in a refrigerator, 

 one in a cellar, one in a warm room, and place the fourth one near 

 a furnace or a stove. Record the number of seed used in each 

 case and calculate the percentage of germination for each kind of 

 seed and at each temperature. Ascertain the approximate tem- 

 perature in each case by means of a thermometer. Repeat the 

 experiment with reference to light by placing one tumbler where 

 it will have sunlight, another in the light of the window but where 

 sunlight cannot reach it, a third one in a darkened room, and the 

 fourth one in a dark cellar; and note the results. From this 

 experiment we see that light is likewise an important factor in 

 germination. 



EXERCISES 



1. Secure a weed or some other plant and make a drawing of it, showing 

 the roots, stem, branches, and leaves. 



2. Estimate the amount of root surface and compare this with the 

 amount of leaf surface of the plant secured. 



3. Secure a flower, make a drawing showing its various parts, and give 

 their names. 



