292 



Introduction to Botany. 



broken away the spores are still kept from falling out by 

 means of a fringe of teeth (Fig. 150, C) ; these are more or 

 less hygroscopic in different species. 

 They close the opening of the cap- 

 sule in a humid atmosphere and 

 open outward to allow the spores to 

 be shaken out in a dry atmosphere. 

 The winds probably dry the teeth 

 and shake out the spores at the 

 same time. 



FERNS. 



FIG. 153. 



179. Character of Ferns. An 

 examination of the construction of 

 a fern shows it to be much more 



Scolopendrium, a fern bearing hi g hl y Organized than a niOSS. The 



oblong clusters of sporangia tissues of its stem and leaves are 



(sort, singular sorus} . After -i rr . . . i . r 



STRASBURGER. differentiated to perform separate 



functions, as we have seen to be the 



case in the higher plants, and it has true roots. The leaves 

 not only perform the usual photosynthetic function of 

 green leaves, but they 

 may also bear spores 

 asexually on their under 

 surface (Fig. 153); and 

 since no part of the fern 

 plant bears sperms or 

 eggs, we must look upon 

 it as an asexual genera- 



r IG. I54 



tion, or sporophyte, 



. J Cross section through a sorus of Scolopendnum. 



Which in the moSS we a and d, sporangia containing spores (the 

 Saw tO be leafless spore is the unicellular stage of the gam eto- 



phyte) produced asexually ; c, the protective 

 (namely, the Capsule covering or indusium. After STRASBURGER. 



