AND IRRITABILITY OF SENSITIVE PLANTS 2 1 1 



The night sleep of the leaves of the Partridge Pea is very pronounced, 

 the leaflets folding upward and the whole leaf drops through an angle 

 of 65 to 75 degrees. The paraheliotropic response is equally marked. 

 At a temperature of 21 to 23° C. the leaflets arc fully expanded; when the 

 temperature rises to 26 or 27° C. the leaflets close ^ 2; at 31 to 32° C. 

 the leaflets are ^ closed, and at 33 to 35° C. complete closure is observed, 

 with a drop of the entire leaf. 



Not only are the leaves of C. chamaecrista sensitive to hght stimuli 

 but also to other forms of stimulation. WTien leaflets are stimulated 

 mechanically they begin to close after a latent period of 3 to 4 seconds, 

 at a temperature of 27° C. after the first stimulus the leaflets close 

 yi and the leaf drops through an angle of about 25 degrees, the move- 

 ment continuing during a period of 1 minute. A second stimulus is 

 then applied and after a latent period as before the leaflets close % 

 that is they will have moved through an angle of about 60 degrees; 

 the leaf drops through an angle of 15 degrees. On the application of a 

 third stimulus, a latent period of 2 to 3 seconds ensues, the leaflets 

 move through an additional angle of 20 degrees and the leaf drops 8 

 to 10 degrees further. The leaflets are now almost closed and additional 

 stimuli cause no change in their position. Here, as for Desmodium 

 canescens, a summation of stimuli is required, but fewer stimuli are needed 

 than in the latter plant to cause closure of the leaflets. The leaf re- 

 expands in 14 to 18 minutes. The leaflets are equally sensitive to 

 chemical stimuli. 



That the gland on the petiole is an irritable center was shown in 

 experiments with certain chemicals by Professor Macfarlane (Lecture 

 Notes). When he placed a drop of turpentine or alcohol or 60 p.c. sul- 

 phuric acid on the basal gland of a leaf with 13 pairs of leaflets, the 

 upper 8 pairs closed rapidly, the lower 5 passed slowly through an angle 

 of 40 degrees. 



Leaflets. Continuous lines of crystals are present along the veins 

 of the leaflets — two to five rows according to the size of the vein. The 

 crystals are large, regular, hexagonal rhombohedra, and are so placed 

 in the cells as to have the longer axes of most of them parallel to the 

 direction of the vascular bundle with which they are associated. The 

 average size of the crystals is 15.8 microns long and 9.4 microns wide. 

 Each crystal cell contains one crystal, and is one-third larger than the 

 crystal itself. The protoplasmic sheath in which each crystal is imbed- 

 ded stains deeply with protoplasmic stains, such as eosin or aniline blue. 



