208 STECKBECK— ON COMPARATIVE HISTOLOGY 



gonal prismatic form is more in evidence than in the former species, 

 and in the pulvini are fewer crystals than in D. rotundifolium. 



Desmodium paniculatum 



In distribution, in relative sensitivity, and in histological details 

 this species resembles very closely the two Desmodiums just described. 

 In the crystal sheaths of the leaflet bundles there is a decided increase 

 in the twin rhombohedral crystals. The line across the middle of these 

 six angled crystals is more evident in a greater number of crystals than 

 for any plant studied so far. The crystals on an average are consider- 

 ably larger than in D. Dillenii and D. rotundifolium. 



Desmodium canescens 



Of the native species of Desmodium studied, this is the most sensitive 

 in its leaf movements. Both the nyctitropic and the paraheliotropic 

 responses are most marked. When mechanical stimuU are applied 

 the leaflets drop after a rather long latent period. In one experiment 

 the median leaflet was stimulated by giving it a slight blow. After a 

 latent period of 80 seconds, it dropped through an angle of about 20 

 degrees; 90 seconds after the first stimulus a second was given, followed 

 by a further drop of the leaflet. A third and a fourth stimulus were 

 applied with a 90 second interval between them. In all as a result of 

 the four stimuli the leaflet dropped about 70 degrees. Dr. Macfarlane 

 (30) states that the leaflets respond to chemical stimuU. A 6% ether 

 solution applied to 8 median leaflets caused contraction in aU of them. 

 A drop resulted equally whether the ether was applied to the secondary 

 pulvini or to the general leaf surface. A latent period of 1 to VA min- 

 utes followed the application of the ether. 



Leaflets. The crystals along the leaflet bundles are arranged in 

 fairly continuous lines, with few breaks in the continuity of the crystal 

 cells. The more uniform regularity in the shapes of the crystals and 

 their larger size, as compared with those in the other species of Des- 

 modium is very marked (Plate LX, Fig. 8). The majority of the crystals 

 are of the six angled prismatic type, with the partition line across the 

 middle of most of the crystals evident. Polarity of arrangement of 

 the crystals is more marked than in the other species of Desmodium. 



Pulvini. Elongated, prismatic crystals are scattered throughout 

 the cortex in both primary and secondary pulvini. In the endodermal 

 region of the pulvini a greater abundance of crystals is present than 



