220 



BOTANY. 



are perennial, in some cases, however, dying down to tne 

 ground at the end of the summer, the underground por- 

 tions alone surviving the winter. 



Fig. 128.— J^, the sexual plant of a fern, under side ; &, root-hairs ; an, 

 antherids ; or, archegones. JJ, the same after fertilization, showing the 

 growth of the f ernlet (asexual plant) ; 6, its leaf ; w', its first root. Mag- 

 nified a few times, 



409. The sexual plant of ordinary ferns is small (3 to 4 

 mm.), somewhat heart-shaped, and generally provided with 

 root-hairs on its under surface, by means of which it secures 

 nourishment for its independent growth (Fig. 128. A). 

 In the Pepperworts the sexual plant is so reduced as to be 

 only a small outgrowth from the germinating spore. 



410. The sexual organs develop on the under side of the 

 gametophore (Fig. 138, A). The antherids are nearly 

 globular, few-celled structures (Pig. 129, A) consisting of 

 an outer layer of cells surrounding a central mass which 

 produces the antherozoids. "When mature, they rupture 

 and permit the escape of the spiral antherozoids (Fig. 

 129, C) which swim with a rotary motion. 



411. The archegones (Fig. 130) are flask-shaped organs 

 sunken into the tissues of the plant. At first the neck is 

 closed, but at maturity it opens down to the germ-cell 



