AND IRRITABILITY OF SENSITIVE PLANTS 209 



toward the surface, and here in addition to the elongated type, the kind 

 so typical for the leaflets is noted. 



Desmodium gyrans 



Next to Mimosa pudica there is probably no sensitive plant that has 

 been studied more extensively than Desmodium gyrans. The autono- 

 mous movements of the lateral leaflets have been known and studied 

 for several centuries. These oscillating movements are often so rapid 

 that they may be readily followed with the naked eye. The larger 

 terminal leaflet performs well marked nyctitropic, as well as less notice- 

 able oscillating movements. The irregular twitching movements of 

 the lateral leaflets have given the name Telegraph "Plant to this species. 



Leaflets. The crystals in the bundles of the lateral and the terminal 

 leaflets are very abundant, forming continuous lines. The number 

 of lines varies with the size of the veins with which they are associated. 

 The crystals are practically all of the very regular six-sided, prismatic 

 type. There is a greater abundance of crystals in the lateral than in 

 the terminal leaflets. 



Pulvini. In both primary and secondary pulvini, the kinds of crys- 

 tals and their distribution in the cortex are similar to that described 

 for D. canescens. The elongated rhombohedral type of crystal is here 

 the dominant one. 



Petiole. A great abundance of regular prismatic crystals is present 

 along the vascular bundles of the petioles. So great is the number of 

 these crystals that they form a broad continuous sheath over the bun- 

 dles. In nyctitropic response the petiole moves upward from the day 

 position. 



Amphicar paea monoica 



This common leguminous plant, the Hog Peanut, abounds in eastern 

 North America from Canada to Mexico. The thin tri-foliate leaves 

 are sensitive to Hght and to mechanical stimuli. The day and night 

 positions of the leaflets are fully described by Schively (42, p. 308). 

 Usually 4 to 5 mechanical stimuli are required to cause the leaflets to 

 drop through an angle of 70 to 75 degrees. Leaflets that have been so 

 stimulated will recover the original position in 13 to 16 minutes. The 

 latent period, the summation required, the response period, the neutral 

 period and the re-expansion period, are all about the same, or slightly 

 shorter, as for Desmodium canescens. 



