222 STECKBECK— ON COMPARATIVE HISTOLOGY 



In general, the long axes of the crystals are parallel to the 

 direction of the vascular bundles, but occasionally the crystals lie 

 cross-wise in the crystal cells. 



Pulvini. In both primary pulvinus, and secondary pulvini, a few- 

 large scattered crystals occur in the cortex. These are quite irregular 

 and do not resemble the type of crystal present in the leaf. 



Petiole. The lines of crystal cells in the petiole are of the same 

 nature as those along the veins of the leaflets. Each crystal is im- 

 bedded in a protoplasmic sac. 



Biophytum sensitivum 



This species of Biophytum is another fairly common green house plant, 

 that is native to the Tropics of both the Old and the New World. In 

 structural details and in leaf sensitivity it resembles rather closely 

 B. dendroides, but is slightly more sensitive than the latter. 



The morphological characters of the plant, and the day and night 

 positions of the leaflets, are indicated in the illustration (Plate LXIII, 

 Fig. 18-19). 



Leaflets. As in the preceding species, continuous lines of crystal 

 cells are associated with the vascular bundles of the leaflets. The 

 majority of crystals are of the regular, six-angled, rhombohedral type. 

 Here and there a barrel-shaped crystal is noted in the lines of crystals. 

 In the fully developed leaflets, each crystal fills % of the lumen of 

 the cell in which it is contained (Plate LXIV, Fig. 24-25). While the 

 leaflets are small, immature and are non-chlorophylloid, or are very 

 pale green, the crystals are relatively small. It is noteworthy that at 

 this stage the leaflets are non-sensitive or very feebly sensitive. Cunning- 

 ham (10) showed that in Mimosa pudica the leaflets do not attain 

 their maximum sensitivity until they have developed the character- 

 istic deep green color. 



Pulvini. The lines of crystal cells end at the beginning of the pulvini. 



Petiole. The crystals are of the same type as in the eaflets, and form 

 crystal sheaths along the vascular bundles. Each crystal is enveloped 

 in a protoplasmic sac, with fine connecting intercellular threads between 

 the adjacent crystal cells. 



Nature of the Crystals 



The crystals present in the two families studied — Leguminosae 



and Oxalidaceae — consist of calcium oxalate, as was proved by applying 



various chemical tests. Very thin fresh sections were used in the tests. 



It is important to use thin sections so as to have the crystals exposed 



