210 STECKBECK— ON COMPARATIVE HISTOLOGY 



The crystal distribution in Amphicarpaea monoica is emphasized by 

 Schively (42, p. 358), who writes: — "In early development numerous 

 crystals appear in the cells forming the inner row of the cortex of the 

 stem. These ultimately constitute a distinct crystal sheath. The 

 crystals are somewhat prismatic in form, possessing an apparent parti- 

 tion across the middle. These twin structures occur also round the 

 vascular areas of the leaves, and also in the cortex of the pulvini. " 



The writer compared very carefully the crystals in the first formed, 

 simple, opposite leaves, and the later formed pinnately trifoliate leaves, 

 and found the crystal system better developed in the compound leaves. 

 The crystals are more abundant, larger, and the crystal Unes are more 

 continuous than they are in the simple leaves. 



From experiments made on the relative sensitivity of the two kind 

 of leaves, the writer found the simple leaves more sluggish in their move- 

 ments. These experiments were made May 14, when the simple leaves 

 were fully expanded, while the compound leaves were not fully devel- 

 oped. The younger condition of the compound leaves may explain 

 their apparent greater sensitivity, for younger leaves always show quicker 

 response than do those that are older. 



Cassia chamaecrista 



This species of Cassia and two others are northern outlying repre- 

 sentatives of a large tropical and sub-tropical genus, which includes 

 more than 300 species. C. chamaecrista, the Partridge Pea, is found in 

 sandy soil throughout the eastern United States from New England 

 southward and westward to Texas. This form is quite abundant in 

 New Jersey, where it is often found growing with the next species, 

 Cassia nictitans, from which it can be distinguished by its larger flowers. 

 The Cassias are remarkably sensitive in their leaves, representing the 

 most highly developed types of sensitivity among our native sensitives. 

 The leaves of C. chamaecrista are evenly pinnate with 9 to 15 pairs of 

 leaflets on each leaf. A short almost sessile gland, 1 mm. high, is present 

 on the petiole, close to the primary pulvinus. The top of the gland is 

 elliptical, or oval, in outline, slightly concave, and about 1 mm. long. 

 The primary pulvinus is well developed, as are the secondary pulvini 

 at the bases of the leaflets. The gland, as well as the leaflets and the 

 pulvini, are irritable. In the superficial cells of the gland the appearance 

 is as in the pulvini, to be described later — there being rather dense masses 

 in each cell (Plate LXV, Fig. 26). 



