202 STECKBECK— ON COMPARATIVE HISTOLOGY 



compound leaf. At the base of the petiole there is a primary pulvinus, 

 and at the base of the lamina a secondary pulvinus, both of these only 

 slightly thicker than the petiole. The leaves are very feebly responsive 

 to mechanical stimuh. Only after numerous stimuli (as many as 15 

 or 20) do the two lobes of each leaf rise through a small angle. Marked 

 nyctitropic response is shown, the lobes at night moving upward 

 through an angle of 80 to 90 degrees. There is also a slight drop of 

 the entire leaf from the day position. 



Leaf. Scattered throughout the mesophyll of the leaves are a 

 number of conglomerate crystals (Plate LIX, Fig. 5). In addition to 

 this type there are prismatic crystals arranged in discontinuous single 

 rows along the veins. This latter type shows considerable variation 

 in the shape of the individual crystals. Some are irregularly rounded 

 and in general outline resemble the scattered conglomerates; others are 

 regular prisms, usually four or six angled. The hexagonal form is 

 rather rare. The distinct cross-line, so well seen in crystals of the more 

 sensitive plants, is indicated very faintly on a few of the six-sided 

 crystals. The crystals are small, rarely more than 9 microns long. 

 The breaks in the hnes of crystals are shown (Plate LIX, Fig. 5). 



Pulvini. In both the secondary and the primary pulvini conglomer- 

 ate crystals are scattered through the cortex, but none along the vascu- 

 lar bundles. 



Petiole. In the petiole lines of crystals occur regularly in the endo- 

 dermal cells surrounding the vascular bundles. In some cases only a 

 few crystals occur, or there may be twenty or even more crystals in a 

 line, then a break, then another line and so on. The crystals are rather 

 small as compared with the size of the cells in which they are found. 

 A thin protoplasmic sheath surrounds each crystal. 



Gleditschia triacanthos 



The genus Gleditschia is essentially tropical and sub-tropical in its 

 geographical distribution, being represented in tropical Africa, tropical 

 and sub-tropical Asia, sub-tropical Argentina, and in eastern and 

 southern North America. 



G. triacanthos, the Honey Locust is indigenous over a wide region 

 from southern Canada to Texas. The pinnately compound leaves 

 show slight nyctitropic movement. In no case has the writer observed 

 a drop of the leaflets of more than 30 degrees. Rather feeble parahelio- 

 tropic movements have been observed, and no response to other forms 



