304 



The Living Plant 



male cells. In most of the Seaweeds (or Algae), of both salt and 

 fresh water, both kinds of sexual cells are cast out into the water, 

 where those from different plants become completel}^ com- 

 mingled, especially under action of currents, waves, and the 

 I power of the male cells to swim freely 



1 J kgr??^^ about ; and apparently mere chance under 



these conditions is enough to ensure a 

 sufficiency of crossing between different par- 

 ents, although, for all we know, elaborate 

 physiological arrangements, comparable 

 with some of those which will presently 

 be described for the higher plants, may 

 exist to prevent union of sex cells pro- 

 duced by the same plant. Such arrange- 

 ments, indeed, are known to occur in the 

 higher kinds of plants fertilized in the 

 Fig. 106.— Cells from dis- Water, uotably the Ferns, where the male 

 tSc^'tii^'L^ a"d female sex cells produced on the same 

 fied, showing the forma- plant Hpeu at different times. Again, in 



tion of a fertilization tube. 



(From the Chicago Tc.rt- somc other kiuds of low Water plants, whose 



habits are such that the many long threads 

 of which their bodies consist live tangled or felted together, slender 

 tubular projections (a kind of premonition of the pollen-tube), 

 grow out and connect one thread with another (figure 106) ; and 

 through the passage thus formed the contents of one cell can 

 unite with another in cross fertilization, though plenty of cases 

 are known in which the same method is used in the fertilization of 

 one cell by another within the same thread. 



While the Seaweeds, or Algae, are the distinctive plants of the 

 waters, a good many kinds of Flowering plants, originally in- 

 habitants of the land, have been forced into life in the water, 

 developing, of course, appropriate adaptations thereto. Of these, 

 the conspicuous kinds, like the Water Lilies, secure their cross 

 pollination by the very same methods as the showy-flowered 



