LIFE II I STORY OF THE FERN 



371 



Figure 398. — Forked Veins of Fern. 



is the vein of the leaf. During certain seasons of the 

 year, lines form along the margin of the under surfa 

 of the leaves. These lines are made up of many minute 

 reproductive bodies, the 

 sporangia ( sj >6r-an'jl-a : 

 Greek, spore, seed; <m- 

 geion, vessel). Each 

 sporangium contains 

 numerous spores. In 

 some ferns the sporangia 

 occur in dots, the sort 

 (singular, sorus; Greek, 

 ^oros, heap). See Figures 

 396 and 397. 

 ' 262. Life History of 

 the Fern. — The fern 

 plant just described 

 forms spores in the sporangia. These spores tall to the 

 ground and soon begin to grow. The sprout from t la- 

 spore is in the form of a single thread and is a protonema. 

 From the fern protonema there develops a small, flat, 

 heart-shaped body called the proihallium (Greek, pro, 

 before; thallos, twig) which is indispensable to the life 

 of the fern. On the under surface of the ji thallium 



grow small bodies, the antheridia 

 and archegonia. The ant heridia 

 produce numerous motile sperm 

 cells, and each archegoniura a 

 single ess cell. A sperm cell, 

 .hi finding an archegoniura, 

 enters, fuses with the egg cell, 

 and forms the fertilized egg cell. The prothallium La the 

 fern gametophyte. See section 257. 



When an egg cell is fertilized, it begins to gr«>\\ and a 



Figure 399. — Sporangia. 



