182 



MORPHOLOGY. 



the archegonia. One of them in longisection is shown in fig. 

 225. It is flask-shaped, and the broader portion is sunk in the 





Fig. 226. 

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

 their way down through the slime to the egg. 



tissue of the prothallium. The egg is in the larger part. The 

 spermatozoids when they are swimming 

 around over the under surface of the pro- 

 thallium come near the neck, and here they 

 are caught in the viscid substance which 

 has oozed out of the canal of the arche- 

 gonium. From here they slowly swim 

 down the canal, and finally one sinks into 

 the egg, fuses with the nucleus of the latter, 

 and the egg is then fertilized. It is now 

 ready to grow and develop into the fern 

 plant. This brings us back to the sporo- 



phyte, which begins with the fertilized egg. 



Fig. 227. 



fern 



Fertilization 

 'Marattia). s/, spermato- 

 zoid fusing with the nu- 

 cleus of the egg. (After 

 Campbell.) 



Sporophyte. 



374. Embryo. — The egg first divides into two cells as shown in fig. 228, then 

 into four. Now from each one of these quandrants of the embr_yo a definite 

 part of the plant develops, from one the first leaf, from one the stem, from 

 one the root, and from the other the organ which is called the toot, and which 



