218 STECKBECK— ON COMPARATIVE HISTOLOGY 



species, in regard to the crystals, is that in M. Spegazzini 5 to 7 lines 

 of crystals pass into the bases of the strong, stiff hairs that are scattered 

 over both surfaces of the leaflets. Are these hairs irritable? The 

 writer was unable to prove conclusively that the hairs are irritable 

 centers. Haberlandt (19) states that the hairs of Biophytum are sensi- 

 tive. 



The distinct intercellular connections of the crystal cells can be 

 clearly demonstrated in M. Spegazzini. By staining such cells very 

 deeply, followed by destaining, the threads connecting the adjacent 

 cells stand out quite clearly (Plate LX, Fig. 11). 



OXALIDACEAE 



As in the case of Leguminosae, the writer studied the histological 

 details of certain species of this family, including forms that are native 

 and others that have been introduced from the tropics, and are grown 

 in greenhouses. 



Oxalis stricta 



This common native species exhibits very interesting sensitive 

 movements of its leaflets. The nyctitropic movements were carefully 

 studied by Ulrich (45, p. 226). The same author also noted the para- 

 heliotropic response of the leaflets. Macfarlane (30, p. 189) describes 

 the behavior of the leaflets when mechanical stimuli are applied. 

 ^' After a sharp but delicate mechanical stimulus applied with a pencil 

 or other instrument to a terminal leaflet, a latent period of 33^8 seconds 

 elapses, followed by a period of slow but gradually accelerating con- 

 traction during the next 4 seconds. From the 7 to the 20th second 

 the motion is rapid, but thereafter slows down gradually to the 30th 

 second and then becomes increasingly slow till the 45 th second when 

 the contraction ceases. After 15-18 minutes expansion begins, and 

 a very slow rise can be traced till the leaf regains its expanded state 

 in 45-50 minutes." 



Leaflets. In the leaflets small crystals are distributed through 

 the mesophyll tissue. These vary in shape from some that are somewhat 

 irregular, approaching a conglomerate form, to others that are prismatic 

 — four to eight-angled usually. 



Pulvini. In the secondary pulvini no crystals are present. In 

 the primary pulvinus few large conglomerates are found scattered in 

 the cortical zone. 



Petiole. Large crystals, arranged in irregular lines, are present in 

 the cortex just around the vascular bundles. Some of the crystals 



