354 



BRITISH FLOWERING PLANTS 



type (Fig. 227, also p. 28). The upper face is protected 

 hj a strong smooth cuticle ; the stomata are on the under 

 face, and communicate with an almost closed chamber 

 formed by the rolling back of the leaf margins. This 

 arrangement serves to check excessive loss of water in 

 the exposed situations in which the plant is found, and 

 also prevents clogging of the stomata by the dew or rain 

 which is deposited on the upper face only, and owing to 

 the smooth surface is got rid of as quickly as possible. 



CALLITEICHINE^ 

 Aquatic floating herbs. 



Callitriche 



Inconspicuous monoecious protogynous flowers. Tlie 

 pollen is probably in some cases carried by insects, in 

 others by wind, and sometimes by water. 



Pig. 228. — Male flower, consisting of Fig. 229. — Female flower, consisting of 

 one stamen subtended by a pair of a 4-lol)ed ovary with 2 styles ; bracts 



bracts, v. as in male, v. 



0. aquatica. — The pollen grains, as in some other 

 aquatic plants, have no outer coat (extine). They are 

 lighter than water, and thus may easily be carried to 

 the female flowers. 



