536 



LIFE-HISTORIES 



Fig. 301. — Male-lcru (.-icr also Fig. 170). n, h, gcTmination of .sport'-s show- 

 ing formation of young gametophytes (prothallia), "". (Luerssen.) 



Fig. 362. — Male-fern. A, prothallus, lower side, showing archegonia (ar), 

 antheridia (on), and pseudo-roots (rji). 5. B, same, after production 

 of young .sporophyte, showing first leaf (b) and first root {w). (Schenck.) 



or dry cliniatfs. One of our best developed northern ferns 

 is the Aspidium ah-ead}- studied (Fig. 170, page 179). 



As shown ill Figs. 361, 362, the spore in gcmiiiiatiug produces 

 first a row of cells, the terminal one of which soon divides in such a 

 way as to produce a flat, heart-shaped thallus, which is rich in 

 chlorophyll and sends out from the under side of the older part a 

 number of pseudo-roots. By means of these the rear end is firmly 

 attached to the earth while the lobed end slightly ascends. Finally 

 on the lower surface appear archegonia near the tip, and male 

 gametangia toward the base. The latter and their motile gametes 

 are of the form shown in Fig. 363. The gametes, it will be noticed, 

 are somewhat more highlj' developed than any found among the 

 Bryophyta. That is to saj^ the spiral is larger and the flagella are 

 more numerous. The archegonia, which are like the one shown in 

 Fig. 364, differ but little from the others already studied. After 

 fertilization the egg-cell divides into four (Fig. 365, ,4). The upjier- 

 most of these, by its further growth and division produces the foot (/) 

 the function of which is to act temporarily as an haustorium for the 

 embryo-sporopliyte, and to push it out of the gametophyte and on 

 to the earth. t)no of the lateral cells develops into tlie first root ((r) 

 while the opposite one becomes the growing point of the stem, and 



