THE LIFE OF A FERN. 7 



authors supposed to be an example. However 

 the case may be, the antherozoids find their way 

 at last to the entrance of the tubes of the arclie- 

 gonia, and force themselves in and down to the 

 oospheres, which thus are fertilized. The true 

 growth of the fern, as we see it, now begins 

 from the fertilized oosphere. The roots are 

 formed, and pass downward ; the leaf-bud assumes 

 shape, and, being partially inverted, curves upward, 

 taking its natural position, as shown in PI. 3, 

 Figs. 15-18. The central portion of the prothallus, 

 where the plant-bud starts, grows thicker than the 

 portion nearer the edge, where there is hardly 

 more than one tier of cells. This thickened part 

 is by some authors called the cushion. In some 

 ferns the antheridial cells are found on the outer 

 portion of the prothallus, forming projections 

 there. With the Filmy Ferns (Hymenophyllacece} 

 the structure and mode of growth is in many ways 

 different from these sketched, affording resem- 

 blances to certain genera among the mosses. Al- 

 though there may be several archegonia on each 

 prothalluSy it rarely happens that more than one 

 of them is fertilized : therefore but one plant is 

 usually produced from a single spore. Professor 

 W. G. Farlow has discovered that there is also a 

 reproduction by a sort of budding process, which 

 sometimes takes place on the prothalli of ferns, 

 and is analogous to the office of buds on the 



