396 



BRITISH FLOWERING PLANTS 



themselves to changes in the intensity of light by 



altering their shape. Figs. 

 324, 326 are two palisade cells, 

 seen in section in Figs. 325, 

 327. In diflfused light the 

 grains are hemispherical or 

 even somewhat contracted at 

 the base. In sunshine they 

 flatten themselves out, and 

 thus receive less light.^ 



ALISMACE^ 



6 segments ; 



or indefinite ; 



6, or many 



Fig. 325. Fig. 327. 



Fig. 324.— Palisade cell of Potamo- 

 geton natans in diliused light. 



Perianth of 



stamens 6, 9, 

 ovary with 3, 

 carpels. 



BuTOMUS (Flowering Eush) 

 „ „, „ - Nectar abundant, secreted 



Fig. 32a. — Section of same. i. j.i i r j_i 



Fig. 326.— a similar palisade cell by the base 01 the ovary. 

 in sunshine g umbeUatus.— The flowers 



Fig. 327. — Section of same. . i i c 



are large, rose-coloured, oiten 

 20-30 in an umbel, and about an inch in diameter, with 

 6 perianth leaves, 9 stamens, and 6 carpels. According 

 to Sprengel the anthers all shed their pollen before the 

 stigma is ripe, so that self-fertilisation is impossible. 

 On the other hand, H. Miiller says that the anthers are 

 still covered with pollen when the stigma is ripe. 

 Schulz near Halle found the anthers and stigma ripe 

 simultaneously. In the plants examined by Knuth the 

 six anthers which alternate with the segments of the 

 perianth ripen first and shed their pollen. Then the 

 other three anthers open, and soon after the stigmas are 

 ripe. These are all such good observers that the plants 

 probably difl'er in difi'erent localities or seasons. 



^ See also Oxalis, Lemna, Fagus. 



