68 SrUDIKS OF TUE LEAF 



considerably dried, record tlie result and tiie conclusion as to wliicli 

 surface exhales vapor more freely. 



Experiment 17. — A growing plant of Xasturtiuni, which has been 

 standing for several hours in one position so that the light lias steadily 

 come from one direction, is to be observed. L)o all the leaves face in 

 one direction ? Oi' several leaves ? If so, mark the side of the pot 

 toward which they incline with some distinctive mark {e.g.,A.B. 9.:i< ). 

 Young leaves, or at least those not declining in vigor, should be chosen 

 for record. In the notebook record the position of one of these leaves 

 diagrammaticallv, as seen from above. The diagram will consist of a 

 circle, for the pot; a radial line (marked h). for the petiole of the 

 selected leaf; a line aci'oss the end of this, for the blade; and an 

 arrow (marked If) outside tiie circle, for the direction of the principal 

 body of ligiit. 



Note the attitude of the stem, as seen from the marked side of the 

 pot. Represent it by a diagram : make a straight level line for 

 the rim of the pot; another rising from this, for the stem. Record 

 the time. Now expose the plant to strong light from a new direction. 

 Indicate this on the first diagram by a second arrow (//'). 



Leave till a change is plain. .Vt length indicate tiie position of the 

 selected li'af liy new lines (/e') on diagi'am ], and the attitude of the 

 stem, as seen fi'ora the original sidi! of oliservatifin, by a dotted line on 

 diagram 2. If any movements of leaf blades are discovered, find how 

 far they are due to the curvings of the petioles. 



Experiment 18. — ^o-called sleep movements. 



Xote the position of the leaflets on seedlings of the Sensitive Plant 

 (^{ilnl>f:a puilica') when standing in the light. Now place over the pot 

 can-fully, without jarring tin' plants, a Ijox or blackened I'ell jar, so as 

 to exclude all light. In fifteen minutes or so, uncover carefully. 

 \Miat change in the position o£ the leaves? Oxalis may be used for 

 this experiment. If Lupine or Bean is used, the time will be longer. 

 They may be left in a dark closet over night. 



Experiment 19. — Sensitiveness of Mimosa. 



Use the seedlings of the last experiment. Touch one of the leaflets 

 very gentlj'. Touch others less gently. Note the several effects in any 

 one leaf, and if they occur, the resulting effects on surrounding leaves. 

 Are the cotyledons .sensitive? Select a plant which is still in tlie 

 normally expanded condition. Press a hot needle against one of the 

 cotyledons, without shaking the plant. "Wait for the effect. 



If a large plant is available, apply a match flame to the tip of one of 

 the leaves. Note what parts are affected in succession, and the manner 

 in which the effect travels over the plant. ]\Iea.sure the greate.st di.stance 

 to which the effect is transmitted, and the time taken in transmission. 



This experiment may be done before the whole laboratory division, 

 one plant serving for all. If time and facilities permit, it will be of 



