SELACINELLA SP. 127 



the archegonium with its egg is formed. These spores 

 are produced in specialized sporangia on specialized 

 sporophylls. The sporophylls are gathered into strobili 

 or cones. 



A difficulty for the beginning student in studying 

 plants with two kinds of asexual spores (heteros porous 

 plants) often arises from the fact that the gametophytes 

 are greatly reduced in size and are almost entirely enclosed 

 by the walls of the spores that produce them. It is 

 usually impossible by superficial observation to determine 

 whether the structure is an asexual spore, or a gametophyte 

 enclosed by an old asexual spore-wall. It must always 

 be kept clearly in mind that the spores which produce 

 these gametophytes are neither male nor female, but 

 asexual spores. Spores are called asexual with reference 

 to the way in which they are formed, not with reference 

 to what they produce when they germinate. 



After fertilization has taken place, the oospore begins 

 its germination by means of a wall that cuts it into two 

 cells, one of which elongates and forms the suspensor. 

 This pushes the other one down into the female game- 

 tophyte tissue, where it grows at the expense of food 

 absorbed from the gametophyte and soon forms the 

 embryo, which early shows the rudiments of foot, root, 

 stem, and leaves. The latter three organs gradually 

 break through and emerge from the female gametophyte 

 and the plant soon becomes independent. All these proc- 

 esses except the last often occur before the megaspore 

 has even escaped from the sporangium. If before the 

 embryo emerged it had become dormant while enclosed 

 in the female gametophyte, and the wall of the megaspo- 



