MOSSES. 



247 



as shown in the case of mnium in fig. 280, after the remnant of the arche- 

 gonium falls away, there is seen a conical lid which fits closely over the end. 

 When the capsule is ripe this lid easily falls away, and can be brushed off 

 so that it is necessary to handle the plants with care if it is 

 desired to preserve this for study. 



520. When the lid is brushed away as the capsule dries 

 more we see that the end of the capsule covered by the lid 

 appears " frazzled." If we examine this end with the micro- 

 scope we see that the tissue of the capsule here is torn 

 with great regularity, so that there are two rows of narrow, 

 sharp teeth which project outward in a ring around the 

 opening. If we blow our "breath" upon these teeth they 

 will be seen to move, and as the 

 moisture disappears and reappears 

 in the teeth, they close and open 

 the mouth of the capsule, so sensi- 

 tive are they to the changes in the 

 humidity of the air. In this way 

 all of the spores are prevented to 

 some extent from escaping from 

 the capsule at one time. 



521. Note. If we make a sec- 

 tion longitudinal of the capsule of 

 mnium, or some other moss, we find 

 that the tissue which develops the 

 spores is much more restricted 

 than in the capsule of the liver- 

 worts which we have studied. The 

 spore -bearing tissue is confined to\ 

 a single layer which extends around 

 the capsule some distance from the 

 outside of the wall, so that a central 



Two different stages of young sporogonium of cylinder is left of sterile tissue. 

 a moss, still within the archegonhim and wedg- This is the co lumella, and is pres- 

 ing their way into the tissue of the end of the stem. r 



k, neck of archegonium ; /, young sporogonium. ent in nearly all the mosses. Each 

 This shows well the connection of the sporophyte - . r . r ,., , 



with the gametophyte. of the cells of the fertile layer 



divides into four spores. 



522. Development of the sporogonium. The egg cell after fertilization 

 divides by a wall crosswise to the axis of the archegonium. Each of these 

 cells continues to divide for a time, so that a cylinder pointed at both ends is 

 formed. The lower end of this cylinder of tissue wedges its way down 

 through the base of the archegonium into the tissue of the end of the moss 

 stem as shown in fig. 285. This forms the foot through which the nutrient 



Fig. 285. 



