220 STECKBECK— ON COMPARATIVE HISTOLOGY 



Oxalis bupleurifolia 



Of the different species of Oxalis examined, this is the most sensitive 

 in its leaflets. Each leaf consists of a rather long, flattened petiole 

 a quarter of an inch wide, that bears three small delicate obovate leaflets. 

 In nyctitropic movements, the petiole, as well as the leaflets, occupy 

 different positions from those of the day positions. Darwin (11, p. 328) 

 notes the movement of the petiole. "The foliaceous petiole rose during 

 the day and early part of the night, and fell during the remainder 

 of the night and early morning. " He also observed the movement 

 of the leaflets. Ulrich (45, p. 220) gives results obtained on stimulating 

 the leaflets with mechanical and with electrical stimuli. "When 

 stimulated mechanically the leaflet dropped in 0.75 seconds at a temper- 

 ature of 30° C. Eleven subsequent stimulations were given of equal 

 intensity a minute apart; each caused the leaf to fall slightly lower 

 than the preceding one. The leaflet had entirely recovered in thirty 

 minutes from the begining of stimulation." 



Leaflets. Numerous huge, somewhat irregular crystals are scattered 

 through the mesophyll of the leaflets, with more of these toward the 

 lower surfaces. The crystals resemble very closely those found in 

 0. Ortgiesi, but exhibit greater regularity and uniformity in their shapes. 

 (Plate LXIV, Fig-22). Each crystal is 32-36 microns in diameter. 



Pulvini. The type of crystal found in the leaflet is continued into 

 the small secondary pulvini, but here relatively few crystals are found. 

 In the primary pulvinus a greater number of the large crystals are 

 present scattered through the cortex. 



Petiole. The foliaceous petiole of this plant shows a very interest- 

 ing crystal development, with one to three continuous lines of regular 

 crystals along the ventral side of each of the numerous bundle strands 

 ^extending through the petiole. In shape the crystals resemble the 

 six-angled rhombohedral type so characteristic of the more sensitive 

 members of the Leguminosae, but the angles are not as sharp as those 

 of legumes, and the individual crystal is somewhat barrel-shaped. 

 The line across the widest part of the crystal is very evident in most 

 of the crystals. Each crystal occupies 3^-% of the crystal containing 

 cell, and is en\ eloped in a rather diffuse protoplasmic sac. 



Of the different species of Oxalis that were examined the relation 

 in the petiole of O. bupleurifolia represents the highest development of 

 crystals, that is not including the species of Biophytum which by some 

 writers are included in the genus Oxalis. 



