206 STECKBECK— ON COMPARATIVE HISTOLOGY 



rod shaped type with pronounced transversely projecting processes at 

 both ends. These processes project from both sides of the ends and 

 seem to be of a different composition from the elongated portion of the 

 crystal, for, usually they take a slight stain when protoplasmic stains 

 are applied to the crystal containing cells, while the rest of the crystal 

 remains unstained. Some of the crystals show the partition lines acrsos 

 the middle, as was indicated for some of the larger six angled crystals 

 in the leaflets. The styloid crystals, on an average are of about the same in 

 length as the hexagonal type but quite narrow, from 1.8 ot 5 microns 

 side. In addition to the elongated form few quadrangular crystals 

 occur in the pulvini. In the endodermal region the crystals show a 

 certain polarity of arrangement, in that the longer axes of most of the 

 crystals are in the same direction as that of the bundles. 



In the primary pulvinus of the leaf the crystal distribution differs 

 from that of the secondary pulvini in the smaller number of crystals 

 present in the former. 



Petiole. Both the elongated and the quadrangular types of crystal 

 are found in the petiole, with a larger number of the latter kind. Both 

 are arranged in discontinuous lines in the endodermal zone. The 

 styloid type is most abundant in proximity to the pulvini. (Plate LX, 

 Fig. 7). 



Desmodium rotimdifolium 



The large genus Desmodium, of more than 150 species, is widely 

 distributed throughout the tropics of both hemispheres. Representa- 

 tives of the genus are also found in the sub-tropical and temperate 

 regions. In North America, Desmodiums are found from southern 

 Canada southward. Twenty species are included in the range covered 

 by Gray's Manual. All of these species, as far as studied, show sensi- 

 tivity in their leaflets. The degree of sensitivity varies considerably 

 with the different species. 



D. rotund i folium, of the four species studied, both from the crystal 

 relation and the relative sensitivity, can well be considered as the least 

 specialized. This species is found in the eastern United States from the 

 Canadian border, southward to Louisiana. It is usually found in rather 

 dry woods, where it creeps along the ground. The prostrate habit is 

 given by Macfarlane (30, p. 202) as a reason for the sluggish irrito- 

 contractiHty of this species as compared with other species of the 

 genus. Amphicqrpaea, Desmodium canescens and Desmodium panicu- 



