AND IRRITABILITY OF SENSITIVE PLANTS 213 



applied, the leaflets close further through an angle of 30° and the mid- 

 rib drops 10 to 15 additional degrees. A third stimulus brings very 

 slight additional movement. The leaf so closed re-expands in 9 to 12 

 minutes. 



Macfarlane (30, p. 201) proved that when carbonate of ammonia 

 is applied to the petiolar gland, closure of the leaflets on that same leaf 

 follows. 



Leaflets. The regular lines of cr^'stal cells along the veins stand out 

 very clearly in this species. The crystals are uniform in size and are 

 of the six-angled rhombohedral type. The line across the middle of 

 the crystals is evident. The polarity of arrangement of the crystals 

 with reference to the ^ascular bundles is very marked. The crystals 

 on an average are larger than for Cassia chamaecrista, some attaining 

 a size of 18 microns long and 13.5 microns wide (Plate LX, Fig. 9). 

 The crystals are continued into the apex of the leaflets. 



Pulvini. The regular six-sided prismatic crystals of the leaflets 

 are also present in the pulvini, and are located in the endodermal region. 

 There are relatively few of these crystals. 



Petiole. Throughout the endodermis of the bundles an abundance 

 of crystals is present, forming a continuous crystal sheath, with branches 

 passing into the gland that is present on the dorsal side of the petiole 

 (Plate LXV, Fig. 27). The crystals are very abundant in the lower 

 half of the gland, being massed around the vascular bundle which enters 

 the gland. No crystals are found in the terminal region of the gland. 

 This upper portion of the gland resembles pulvinar structure. In the 

 stem, the crystal distribution is like that in the petioles. The crystals 

 are always present in the endodermis, and are found in all parts of the 

 stem. Branches of crystal cells extend into the base of the cotyledons, 

 but no crystals were observed in the cotyledons themselves. The crystal 

 lines cease at the point in the main axis where the tap root begins. The 

 writer was unable to find crystals in the roots of this plant. 



The crystals of Cassia nictitans show the enveloping sacs better 

 than any plant described thus far. The intercellular connecting threads 

 are also very well brought out. By staining crystal cells in eosin for 

 48 hours, that had previously been fixed in chrom-acetic, and then de- 

 staining rather sharply, the writer was able to demonstrate very clearly 

 the presence of intercellular connections. Good results were also 

 obtained by following Gardiner's method to bring out intercellular 

 connections. By this method the sections are put in iodine solution 

 for 20 minutes, then in strong sulphuric acid for a few seconds; then 



