2l8 



REPRODUCTION 



is anchored to the soil by hair-hke rhizoids, and bears on its 

 under side two sorts of sacs, one the antheridium (Fig. 125, A), 

 containing sperm cells or male gametes, and the other the arche- 

 gonium, B, bearing an egg cell or female gamete. Some pro- 

 thallia, however, bear antheridia only. 



Since the prothallium bears the gametes we call it the gameto- 

 phyte. 



Fertilization of the Egg. — The sperm cells swim by means 

 of their cilia to the archegonia, through the water that gathers 

 under the prothallia (Fig. 125, B), being attracted by a substance, 



Fig. 125. — A, Antheridium containing sperm cells; B, archegonium containing an egg 

 cell which has been found by five sperm cells. All from Osmunda cinnamomea. (After 

 Campbell.) 



probably malic acid, diffusing through the water from its place 

 of secretion in the archegonium. The sperm cell now fuses 

 with the egg. Following this the fertilized egg cell begins a 

 series of nuclear and cell-divisions leading up to the full-grown 

 fern (Fig. 124, E); and this produces sporangia and spores essen- 

 tially as already described for Aneimia. Because of its bearing 

 spores the fern plant is called the sporophyte. 



Interpretation of Processes of Nuclear Division. — The 

 interpretation that is now being put on the behavior of the nuclear 

 substance during division as previously outlined is suggested 

 not only by what we see under the microscope but also by what 

 we observe in carrying on pedigree cultures of hybrids, as will 

 soon appear. We can best lead up to the interpretation by 



