FERNS 



367 



521. Development of the embryo fern plant. The ferti- 

 lized egg is the beginning of the second generation or spore plant 



Fig. 332. 



Mature and open archegonium of fern (Adiantum cuneatum) with sperms making their 

 way down through the slime to the egg. 



(sporophyte) , which is the fern plant as we know it. The egg 

 divides by successive divisions, first into two cells and then into 

 four. These four cells, or quad- 

 rants of the embryo, give rise to 

 four parts of the embryo. The 

 anterior upper quadrant gives rise 

 to the stem, the anterior lower cne 

 to the leaf, the posterior lower one 

 to the root, and the posterior upper 

 one to a haustorium-like organ 

 called the foot, through which food 

 substances are passed from the pro- 

 thallium to the embryo until the 

 latter has established itself on the 

 ground. The egg case grows for a 

 time with the embryo, encloses and protects it. It becomes, 

 therefore, a hood (calyptrd). The root grows quite rapidly, 

 breaks through the hood, and enters the ground. The leaf 



Fig. 333- 



Two-celled embryo of Pteris serrulata. 

 Remnant of archegonium neck below. 



