3) flower. In the 

 case of the male flower both 

 bracts can be seen. (Enlarged.) 



[A. A.] 



xvm] HYDROPHILOUS POLLINATION 237 



Pseudo-callitriche, which consists of submerged plants grouped 

 round the species C. autumnalis. C. autumnalis has no land form, 

 but vegetates, flowers and fructifies 

 below the level of the water surface. 

 Throughout the genus the simple 

 male and female flowers occur separ- 

 ately (Fig. 1 54) ; the female flowers 

 are commonly found lower down the 

 inflorescence than the male, but, in 

 C. autumnalis^ several male and female 

 regions may alternate with one another. 

 Insects, and possibly wind, carry the 

 pollen of the Eu-callitriches, which is 



r . FIG. 154. Calhtnche verna, L. 



of the terrestrial type and is clothed July 19, 1910. Flowering shoot 



with an exine insoluble in sulphuric 



acid. That of the Pseudo-callitriches, 



on the other hand, is of the aquatic 



type; it has no differentiated exine 



and contains oil globules which render it lighter than water. 



It is carried to the stigmas by water currents. 



The aquatic pollination of Ceratofhyllum (Hornwort) has 

 already been considered 1 , as well as that of three members of the 

 Potamogetonaceae, Cymodocea^^ Zoster a* , and Zannichellia^. In 

 connexion with the submerged pollination of Naias graminea 

 also belonging to the Pondweed family a picturesque incident 

 which has been placed on record by Bailey 5 , suggests that 

 aquatic animals may occasionally play a part in the pollination 

 of submerged plants. He writes, " While . . . examining portions 

 of a living plant on which were ripe anthers, I noticed a colony 

 of Vorticellidae attached to one of the fascicles of leaves; the 

 grace and activity of its movements led me to watch it for a 

 considerable time, and whilst so watching it I witnessed grains 

 of pollen whirled in all directions, or drawn into the vortex of 

 the animal by its marginal cilia. The alternate contraction and 



1 See pp. 84-85. 2 See p. 126. 3 See pp. 127-129. 



4 See pp. 70-71. 5 Bailey, C. (1884). 



