THE WOOD SORREL 265 



position are effected by certain tissues becoming more 

 turgid or more flaccid, by absorption or loss of water. 

 According as these tissues are swollen or limp, so 

 the leaflet is held horizontal or sinks to the vertical 

 sleep position. 



It may also be mentioned here that tlie minute 

 chlorophyll grains, which contiiin the chlorophyll 

 (p. 10) or green pigment of the leaf, have the power 

 of changing their position in the cells, according 

 to the intensity of the light. In dull or diff'use 

 light, they spread themselves so as to obtain the 

 maximum illumination. In stronger sunlight, they 

 collect around the walls of the cells, and place them- 

 selves parallel to the rays of light, so as to receive less 

 illumination, while, after long-continued sunlight, they 

 all gather together in groups at the ends of the cells. 



The fruits of the Wood Sorrel are interesting 

 from the fact that the seeds are shot out one by 

 one, often to considerable distances. The pod, or 

 capsule as it is termed botanically, is five-chambered, 

 each chamber possessing two seeds, placed one above 

 the other, and attached to the central column. Each 

 seed possesses two coats. Some of the cells of the 

 inner layers of the external coat, when mature, are 

 in a high state of strain. They become very tense or 

 turgid. When each chamber of the fruit opens, the 

 inner strained layers of the external seed-coat swell 

 up and burst the outer, non-strained layers, and thus 

 the external seed-coat is turned inside out. This 

 violent jerk shoots out the seed itself, enclosed in its 



