146 



DIGITALIS, 



[CHAP. 



firmness with which they are closed, and in the posi- 

 tion of the honey, which lies at the basis of the 

 corolla, and does not penetrate into the short spur, 

 which is hairy, and therefore not suited for such a 

 purpose. They are almost always fertilised by humble 

 bees, though smaller bees occasionally force their way 

 into them. 



Digitalis purpurea (the Foxglove) is also exclusively 

 fertilised by humble bees, which alone are large 



FIG. 10-$. Bartsia odontites. 



enough to fill the bell, and thus to deposit pollen 

 on the stigma. The flower is proterandrous, but 

 appears to be self-fertile if the visits of humble bees 

 are delayed or prevented. The cells of the anthers, 

 as Ogle has pointed out, are at first transverse (Fig. 

 100), but as the two pairs ripen they successively 

 become longitudinal (Figs. 101 and 102). 



