256 



BOTANY OF THE LIVING PLANT 



to their tips, and a single stigma is the result, as in the Lily (Fig. 199) 

 or Datura (Fig. 204). Even here the receptive surface is lobed, and 

 the number and position of the constituent carpels is indicated by 

 that of the stigmatic lobes. From external observation this is often 

 the readiest guide to the composition of the gynoecium. For instance, 

 the two-lobed stigma of the Compositae accords with the facts of 



FIG. 204. 

 Stigma of Datura with pollen-grains adhering to its surface. (After Figuier.) 



development of their flowers, in which two carpels make their appear- 

 ance (Fig. 1 88). In Datura the two lobes clearly indicate the two 

 carpels of the Solanaceae. 



The roughness of the stigmatic surface is due to the outgrowth of 

 the superficial cells as papillae (Fig. 204), the size of which is found to 

 bear a relation to the size of the pollen-grains. The cells are thin- 

 walled, with active protoplasts ; frequently they are moist, or secrete 

 a sticky juice, which helps to detain the pollen-grains in contact with 

 the surface. The grains themselves have sometimes a sticky exterior, 

 which serves the same end. A still more important feature is that the 

 style , by its elongation carries the stigma upwards to a level suitable for 



