20 HOW TO KNOW THE FERNS 



portance to the general student, the fertilization 

 of the egg cell in the prothallus of the Lycopo- 

 dium is carried out on very similar lines to 

 those which have been described in the case of 

 the Fern. 



The life histories of the Selaginellas evidence 

 some important differences which call for 

 special comment. Here throughout the whole 

 family the spore-bearing part of the plant is in 

 the form of very definite cones. As in the case 

 of Lycopodium there is only one sporangium to 

 each leaf, but they are of two kinds. One, on 

 account of the fact that it is responsible for tjie 

 production of small spores, is called the micro- 

 sporangium ; the other, the megasporangium. 

 The two kinds of sporangia are usually present 

 on the same cone, although the microsporangia 

 are as a rule higher up the stem than the mega- 

 sporangia. The number of microspores pro- 

 duced is very large, but only four megaspores 

 are borne in each megasporangium. The mega- 

 spores are, of course, very much larger than 

 the microspores. The germination of the 

 megaspores is started in the sporangium; at 

 a certain point in their development they are 

 shed. In the case of the microspores germina- 

 tion commences after the spores have fallen 

 on to moist soil. The prothallus is exceedingly 

 small, being little more than a group of cells 

 forming an antheridium. Should there be 

 sufficient moisture about, the spermatozoids 

 which are produced by the antheridium swim 

 towards the archegonia in any female pro- 

 thallus which may be near. Fertilization then 

 takes place, and the final outcome is the young 

 plant. Now and again in certain species it is 

 seen that the megaspores develop to such an 

 extent within the sporangium that fertilization 



