290 



The Living Plant 



with a ready fertilization. The structure which has been devel- 

 oped in adaptation to these conditions is in form of a flask-shaped 

 covering to the buried egg-cell (figure 104) ; the end of the tube 

 opens when the egg-cell is ripe and water is present, and exudes 

 a special liquid chemotropically attractive to the spermatozoids, 



FIG. 104. A series of figures illustrating the reproduction of a common Fern. The sexual 

 cells are borne on the under side of a small thin leaf-like part close to the ground. 

 In the lower middle part of the picture is a squarish egg-cell with prominent nucleus, 

 buried in chlorophyllous tissue, and covered with an elongated-tubular structure, 

 down the cavity of which a spiral-shaped male cell is proceeding to unite with the 

 egg-cell. 



which then swim towards and down the neck to the egg-cell. But 

 such plants are as obviously dependent upon water for fertiliza- 

 tion as are the Seaweeds; and hence they are confined to places 

 habitually wet, or must grow so close to the ground that fertiliza- 

 tion can be effected during flooding by rains. Still another step, 

 but this time the final one for plants, in the evolution of secondary 



