Ferns and Their Allies 197 



Within the capsule are formed spore mother cells, each of which forms 

 jour spores, as in the true mosses. At this time the chromosome number 

 is reduced from 2N to N. When the spores are shed in late summer, 

 they germinate to form a flat^ green, heart-shaped prothallus (prothal- 

 lium) with a notch at its anterior end. Rhizoids anchor the prothallus 

 and absorb water and nutrients. The prothallus matures to form a 

 gametophyte which may not be over one-fourth inch in diameter. The 

 same gametophyte may produce male antheridia and female archegonia 

 on its lower surface. 



LATERAL xRIDGE 



EPIDERMIS 



OUTER SCLERENCHYMA 

 INNER SCLERENCHYMA 



PERICYCLE 



PHLOEM 



XYLEM 



ENDODERMIS 



^PARENCHYMA 



VASCULAR BUNDLES 



Fig. 69. — Rhizone (underground stem) of bracken fern. A, one-half of rhizone 

 shown in cross section; B, a vascular bundle highly magnified. 



The antheridia may form on nearly any part of the undersurface, but 

 usually they are more numerous on the older, posterior part where the 

 rhizoids are most abundant. Archegonia are usually limited to the area 

 just back of the notch. Each antheridium is small and dome shaped. 

 Internally there are formed numerous, spiral, multifiagellated sperms 

 (antherozoids) . Each archegonium is small and simpler than it is in 

 liverworts and true mosses. It consists of an enlarged venter, a neck with 

 a canal, and an ^crcr within the venter. 



During jertilization one sperm unites with the egg to form a zygote 

 which develops into a parasitic embryo within the venter. The embryo 

 becomes four lobed and forms the young sporophyte. The lobes develop 

 into four structures: a temporary joot (absorb food), primary root, stem, 



