PROTECTION OF POLLEN. 105 



when they escape from it, and are carried by the water against the long fiHfonu 

 stigmas they adhere to those structures as do the spermatozoids (spermatia) to the 

 trichogyne in the Red Sea-weeds (c/. pp. 60, 61). The filamentous pollen of Halo- 

 phila is even divided by transverse septa into several chambers, or, more accurately, 

 the pollen-cells are aggregated into long strings. The pollen-cells are intercepted 

 under water by the filiform stigmas and grow down them into the ovaries. In the 

 different species of Naias as also in those of Zannichellia the pollen-cells are 

 spherical or ellipsoidal in shape so long as they are inclosed in the anther, but when 

 the anther opens they assume the form of tubes, and are wafted about by the water 

 until they reach the stigmas. The stigma in Zannichellia is triangular and com- 

 paratively large, and owing to the fact that three or four such stigmas have their 

 edges in contact, a sort of funnel is formed, which serves to collect the pollen-cells 

 as they float about. 



The plants above referred to, about fifty species in all, were classed together 

 by the older botanists under the name of Naiadece, but are now grouped into the 

 families of the Potamogetonacese, Naiadacese, and Hydrocharidacese. They are 

 all aquatic plants, but it would be erroneous to suppose that all the members of 

 these groups possess the same kind of pollen as is exhibited by the Grass-wracks, 

 and the various species of Halophila, Posidonia, Cymodocea, Naias, and Zanni- 

 chellia, that is to say, a filamentous pollen destitute of external coat which is con- 

 veyed to its destination by currents of water. On the contrary, thousands of aquatic 

 plants discharge their pollen above the surface of the water and not beneath it. 

 The pollen-cells are spherical or ellipsoidal, have a distinct external coat, and are 

 transported to the stigmas not by flowing water but by the wind or by insects. 

 This is the case even in plants whose leafy parts remain under water throughout 

 their lives. Aldrovandia, Hottonia, and TJtriciilaria, many Pond- weeds (Pota- 

 wiogeton) and Water- crowfoots {Ranunculus), not to mention many others, always 

 raise their flowers above the surface of the water, so that the pollen may escape 

 into the air and be blown or otherwise conveyed from one flower to another. I 

 have observed that even in the case of the various species of Water- star wort (Calli- 

 triche), which were formerly said to accomplish their fertilization under water, the 

 anthers open only in the air, and that the staminal filaments grow in length accord- 

 ing to circumstances until the anthers project above the surface. If they fail to 

 do so, then the anthers of the flowers in question do not open at all; the spherical 

 pollen remains inclosed and decays, together with the anther and its filament, 

 beneath the water. The far-famed Vallisneria (see vol. i. p. 667), too, to which 

 we shall return again later on, only emits the pollen from its anthers into the air. 

 The staminiferous buds, it is true, develop under water; but they detach themselves 

 from the axis of the inflorescence in the form of closed bladders, and do not open 

 until they reach the surface. The stamens then project out of the floating flowers 

 into the air, the anthers burst, and the pollen is set free (c/. fig. 227). If the buds 

 are kept submerged artificially, neither they nor the anthers open, but they decay, 

 and the pollen perishes under the water. And, as in the case of these aquatic 



