500 A TEXTBOOK OF THEORETICAL BOTANY 



The neck canal cells and the ventral canal cell break down into a 

 mucilaginous material which swells and is extruded at the apex of the neck, 

 forcing apart the neck cells and thus opening a passage down to the 

 oosphere. 



Fertilization and Development of the Embryo 



The archegonium, when mature, secretes a substance, probably malic 

 acid, which attracts to it by chemotaxis the actively swimming antherozoids. 

 They make their way down the canal through the mucilage, and one enters 

 the oosphere (Fig. 490) at a clear receptive spot. Fertilization occurs at 



FOOT 



FIRST 

 LEAF 



Fig. 491. — Dryopteris filix-mas. Development of the embryo. A, Four primary segments. 

 B, Periclinal divisions establishing growing points of root, stem and leaf. C and D, 

 Progress of diflferentiation. E, Embryo embedded in enlarged venter of archegonium. 

 F, Embryo emerging from prothallus, primary root turning downwards, primary leaf 

 turning upwards, foot still embedded in prothallus tissue. {After Hofmeister.) 



