AND IRRITABILITY OF SENSITIVE PLANTS 215 



the other leaflet moved, followed by a partial closure of the terminal 

 pair in 20 seconds longer. To cause complete closure of the leaflets 

 2 to 3 stimuli are necessary. The leaf drops 30 to 40 degrees. The 

 re-expansion time of the leaves is 12 to 16 minutes. The small basal 

 secondary leaflets show the same sensitivity as the larger ones, for the 

 same sequence follows when one of them is stimulated, as when its large 

 partner is stimulated. The propagation of stimuli through the stem 

 of this plant is rather limited. If a leaf be stimulated, as described 

 above, the stimulus may be carried to the next leaf above, or occasionally 

 to two leaves in a young shoot. Chemical stimuli in the form of acids, 

 alkalies and alcohol cause a closure of the leaflets. Closure is effected 

 also when heat is applied, or when ice is placed on the leaflets. 



Leaflets. The crystals along the veins are mostly of the six-angled 

 prismatic type, but there are also quadrangular prisms present. The 

 Hnes are fairly regular, but occasionally gaps are noted in the continuity 

 of the crystal cells. Usually a crystal fills }4 to H oi the lumen of the 

 cell in which it is contained. A fairly diffuse protoplasmic sac envelops 

 each crystal. 



Pulvini. No crystals were observed in any of the pulvini. This 

 is the first of the sensitives described so far in which no crystals, neither 

 prisms nor conglomerates, are present. The structural details of the 

 pulvini resemble very closely those for Mimosa pudica. 



Petiole and Stem. Continuous crystal lines extend through petiole 

 and stem in the endodermis. The crystals are mostly the six-angled 

 rhombohedral type, or the quadrangular type, very much the same rela- 

 tion as in the leaflets (Plate LX, Fig. 10). Occasionally an elongated, 

 rather narrow, styloid-like crystal is observed in the lines of crystals. 

 This form is of the type already noted in Robinia and Pueraria, and 

 as noted for those plants, has projecting processes at the ends of the 

 crystals. It is noteworthy that all three forms of crystal, in some of 

 the individual crystals, show the partition across the middle. This 

 would indicate that they are in afl probability twin crystals. The 

 occasional presence of two crystals in the same cell, as noted before, 

 further points to the same conclusion. 



Mimosa pudica 



There is probably no sensitive plant that has been observed for so 



long a time and has been studied more extensively than Mimosa pudica— 



the Sensitive Plant. It is of good size, with quite large bi-pinnately 



compound leaves that show irrito-contractihty to a high degree. On 



