138 



BRITISH FLOWERING PLANTS 



tribution of the chlorophyll corpuscles in the shaded 

 leaflets and those exposed to the sun. In diffused 

 daylight the chlorophyll grains arrange themselves so 

 as to receive the largest amount of light (Fig. 81, a); 

 if the sunshine becomes stronger they collect on the 

 cell-walls parallel to the rays, so as to receive less 

 (Fig. 81, b) and if it continues they finally collect 

 in lumps at the ends of the cells (Fig. 81, c).^ This 

 wonderful power of adaptation only exists in certain 



species. 



The flowers 



are 



homogamous. 



They bend over 



Fig. 81. — Arrangement of tlie chlorophyll grains from the lower parenchymal layer 

 of O^calis Acetosella : ct, in diffuse light ; h, in sunlight ; c, in long-continued 

 smilight. 



in wet weather. The nectaries are five fleshy pro- 

 jections at the bases of the petals, but the flowers 

 are not much visited by insects. They are open, 

 according to Kerner, from 9 a.m. to 6 p.m. The plant 

 also produces cleistogamous flowers, first observed by 

 Michelet." The style varies considerably in length, 

 showing perhaps a tendency to dimorphism. As so 

 often happens with cleistogamous flowers, they bury their 

 seeds in the ground. 



When the flower fades the peduncle turns down- 

 wards, and the flower's head conceals itself among the 

 leaves. When the seeds are ripe it straightens again, 

 and then lifts the capsule well above the leaves. 



. ' For a similar case see Lemna ; for one iu -whieli the form of the grains 

 changes see Potamogeton ; for a cliange in the structure of the leaf see the 

 Dandelion and Fagus (the Beech). 

 ^ Darwin, Forms of Flowers. 



