236 APPLIED BIOLOGY 



root-hairs (rhizoids), which act like true roots of seed-plants 

 in absorbing from the soil. The cells of the prothallium 

 are green with chlorophyll-bodies, which are able to make 

 starch as do ordinary leaves. In fact, the great growth 

 from a minute spore to a prothallium, which may be more 

 than one eighth inch in diameter, is due largely to the 

 materials made by the chlorophyll-bodies, supplemented by 

 some mineral and nitrogenous materials absorbed by the 

 root-hairs from the soil. 



In order to get prothallia for study, one should visit green- 

 houses where ferns are grown from spores. Sometimes they 

 will be found on the surface of the soil beneath ferns kept in 

 moist atmosphere, as in a fernery (a glass-covered case for 

 keeping plants in a moist atmosphere). 



225. Sex-organs of the Prothallium. In most species of 

 ferns, each prothallium develops on its under side both male 

 and female sex-organs for the production of egg-cells and 

 sperm-cells. Each female organ (ovary, or usually called 

 archegonium in ferns and mosses) is a tube-like structure 

 (Fig. 72, F), containing in the expanded base of the tube 

 an egg-cell or ovum. Each male organ (spermary, or an- 

 theridium) is a spherical body, in whose central cavity are 

 produced many spiral-shaped cells with a group of cilia 

 (Fig. 72, D, E) . These are the sperm-cells (also called sper- 

 matozoids), and the lashing movements of their cilia cause 

 them to swim in drops of water on the under side of the pro- 

 thallium to the mouth of an ovary. The tube or neck of 

 the ovary is filled with a mucilage-like material, through 

 which the sperm-cells swim to the egg-cell. One sperm- 

 cell unites with an egg-cell, thus accomplishing fertiliza- 

 tion. Notice the similarity to the fertilization of the frog's 

 eggs ( 58). 



Compared with fertilization in seed-plants (described in 

 189), the sperm-cell of the fern obviously has the same 

 function as the cell which moves down the pollen-tube to 



