252 EXPERIMENTS WITH PLANTS 



themselves out on the ground as in the Dandelion 

 (experiment by placing a Dandelion upside down with 

 its root wrapped in moist cotton) . Study the unrolling 

 of Fern leaves. 



In this connection let us consider the general con- 

 ditions of growth. Every one is familiar with the ex- 

 pression " growing weather," which clearly indicates 

 that growth depends on certain conditions. We may 

 experiment on three of these — namely, warmth, mois- 

 ture and light. For this purpose obtain a lot of seed- 

 ling plants (of the same kind) as similar as possible 

 in respect to vigor and general condition. They must 

 be grown in pots or boxes. 



{a) Temperature. — Select three pots, and mark the 

 stem of each plant with ink two inches from the tip. 

 Cover each pot with an opaque cover (a pasteboard 

 cylinder or box will answer), to exclude the light. 

 Insert a thermometer, if possible, in each, so that it 

 may be conveniently observed. Place one pot in the 

 warmest spot about the building, another in the 

 coolest, and the remaining one in a place of medium 

 temperature. After three or four days, measure tlie 

 growth of each. 



(&) Moisture. — Use two potted plants, provided 

 with opaque covers to exclude light, keeping them 

 all together in a spot where the temperature is most 

 favorable to growth. Before commencing the experi- 

 ment, allow one of them to suffer from lack of water, 



