AND IRRITABILITY OF SENSITIVE PLANTS 201 



duced as a hardy, perennial twiner. It bears large trifoliate leaves 

 that show paraheliotropic and nyctitropic responses to a marked degree. 

 When the temperature rises to 32° C. or higher, the leaflets turn their 

 edges toward the sun. On account of the huge size of the leaflets, often 

 7 or 8 inches long, and 4 or 5 inches wide, the paraheliotropic effect is 

 ver\' striking. The night sleep of the leaflets is equally prominent. The 

 leaflets drop in the nyctitropic movement. 



Leaflets. The cr\'stals in the leaflets are of the styloid type (Plate 

 LIX Fig. 3) and are mainly distributed along the veins, with a few 

 scattered through the mesophyll tissue. The cr\'stals along the veins are 

 arranged in broken lines, with rather wide gaps between the crystals. 

 Each crystal is rod-shaped with short projections at each end, at right 

 angles to the long axis of the cr\-stal. The average dimensions of the 

 cr}'stals are 11.4 microns x 5.65 microns. 



Pulvini. Crystals are found in the primary pulvinus and in the 

 secondary pulvini of each leaf. The type of crystal is similar to that 

 found in the leaf (Plate LIX, Fig. 4). The greater number of crystals 

 in the pulvini are present just around the vascular bundle cylinder, with 

 scattered crystals throughout the cortex from the bundles to the epi- 

 dermis. Here and there a cr>^stal is found with a faint line across its 

 middle portion, at right angles to the long axis. This is the beginning 

 of the twin-cr\stal t>-pe so characteristic of the more sensitive plants. 



Petiole. The rod-shaped, or slyloid-like cr\'stals are also present 

 in the petioles, but in smaller numbers relatively than in the pulvini. 

 In addition to these crystals there occur in the petiole a second type, a 

 rhombohedral form. The latter kind of crystal occurs along the bun- 

 dles in the endodermal region. Here the crystals are arranged in 

 discontinuous lines. The individual crystals are considerably smaller 

 than the cells in which they occur, each crystal occupying about one- 

 half of the lumen of the cell in which it is contained. The longer axis 

 of these cr>^stals is parallel to the axis of the vascular bundles. 



Bauhinia diphylla 



The genus Bauhinia belongs to the sub-family Caesalpinioideae of 

 the Leguminosae, comprising about 150 species, distributed throughout 

 the tropics and the sub-tropics of both hemispheres. B. diphylla is a 

 native of India, growing at rather high elevations. This plant, which 

 is often grown in green houses, bears simple, deeply two-lobed leaves. 

 The single leaf probably represents the terminal leaflet of an originally 



