20 



ON NAIAS GRAMINEA DEL., VAB. DELILEI MAGNUS. 



free pollen, my home observations leave me no doubt that pollen is 

 carried to the pistilliferous flowers by the current ; in such case the 

 plant would be hydrophilous. While, however, examining portions 

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

 Vorticellida 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 elongation of 

 the elastic and thread-like pedicles of the colony kept the pollen- 

 grains in constant motion, which left me no doubt that at times the 

 grainB would be directly borne to the stigmatoid appendages of the 

 pistilliferous flowers. 



The canal- water is most prolific in animal life ; beetles, molluscs, 

 leeches, rotifers, polyps, larva? of insects, &c, must surely prove 

 potent factors in transporting pollen not only in the tepid water of 

 the Eeddish canal, but in the still water of pools and ditches. If 

 we carefully look for instances of their intervention we cannot fail 

 to find distinctive protozophilous plants, dependent for their ferti- 

 lisation upon animal life in the aqueous world, in much the same 

 way as we find entomophilous plants in the aerial world. 



It is a very happy circumstance that Sir Joseph Hooker should 

 have indicated the forms of pollination which prevail in many 

 of our native plants, where known. Sprengel, Darwin, Miiller, 

 Lubbock, Kerner, and many others have largely increased our 

 knowledge of this subject for terrestrial plants, but its extent after 

 all is very limited ; we have but ascended a few steps leading up to 

 the vestibule, whilst the great temple of truth is beyond. While, 

 as regards aquatic plants, and particularly those which are wholly 

 submersed throughout their lives, like Naias graminea, Stratiotes, 

 &c, our knowledge is even more and more limited. Hence Sir 

 Joseph Hooker has earned the thanks of British botanists by 

 bringing into prominence, in his ' Student's Flora,' this important 

 feature in the economy of our native plants. 



XIV.— The Fruit. 



Up to the time of the fer- 

 tilization of the ovule the outer 

 membrane of the flower — the 

 perianth, and the investing 

 membrane of the ovule con- 

 tained within the perianth, 

 both remain transparent or 

 semi-transparent. After pol- 

 lination has taken place the 

 membrane of the ovule be- 

 comes turbid and thickens, 

 while the ovule itself enlarges 

 and becomes a mature fruit, 

 covered with a testa formed of 

 thick-walled cells (figs. 81 to 

 83). 



Fia. 81 



Fia. 83. Fia. 



