PROTECTION OF POLLEN. 105 



chen they escape from it, and are carried by the water against the long filiform 

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

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

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

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

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

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

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

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

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

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

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

 IS they float about. 



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

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

 'amUies of the Potamogetonacese, Naiadacese, and Hydrocharidacese. They are 

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

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

 md the various species of Halophila, Posidonia, Cyraodocea, Naias, and Zanni- 

 ■hellia, 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 

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

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

 ransported to the stigmas not by fiowing water but by the wind or by insects. 

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

 heir lives. Aldrovandia, Hottonia, and Utricularia, many Pond-weeds {Pota- 

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

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

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

 lave observed that even in the case of the various species of Water-starwort (Galli- 

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

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

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

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

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

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

 re shall return again later on, only emit-s the pollen from its anthers into the air. 

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

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

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

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

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

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



