ISOETES 153 



Compare it with Polypodium vulgare in this 

 respect. 



THE GAMETOPHYTE 



The germination of the spores and the development 

 of the male gametophyte from the microspore, and of the 

 female gametophyte from the megaspore, are very 

 difficult to follow, and will be omitted here. The struc- 

 tures of the gametophytes, and the process of sexual re- 

 production should be carefully studied in a text-book, 

 and demonstrated by the instructor, if material is available. 

 E.* Nutrition and Growth: 



1. Is the gametophyte at any stage dependent upon 

 the sporophyte? The sporophyte upon the gameto- 

 phyte? (Consult a text-book.) 



2. It is important to remember that: 



(a) The microspore begins to germinate before it is 

 set free, dividing into two cells, a large one and 

 a small one. The smaller cell constitutes the 

 entire vegetative portion of the male gameto- 

 phyte. The larger cell develops into an an- 

 theridium, consisting of four wall-cells, and four 

 central cells. Each of the latter develops into 

 a multiciliate, spirally coiled sperm, resembling 

 those of the true ferns. 



(b) The megaspore begins to germinate after it is set 

 free. It never develops chlorophyll-bearing 

 tissues. In germination the nucleus divides 

 into about 50 nuclei before any cells are formed. 

 The cells begin to be organized about the 

 nuclei, forming a small-celled tissue in the apex 

 of the spore (where the three ridges meet), 

 and a larger-celled tissue below. Archegonia 

 then develop in the small-celled tissue, and the 



