154 Minnesota Plant Life. 



the conditions are favorable for spore-dissemination they separate 

 from each other a little and allow the spores to scatter out be- 

 tween them. But when the conditions are unfavorable they close 

 over the slit and the spores are not permitted to escape. The 

 ring of teeth is one portion of the automatic spore-distribut- 

 ing machinery of the capsular plant and the twist in the stalk 

 is another device which plays its part in the perfected mechan- 

 ism. Under varying states of moisture the stalk slowly twists 

 and untwists so that the mouth of the nodding urn is carried 

 through a circle dispersing its spores as it turns from side to side. 

 Such an apparatus insures the dissemination of spores toward 

 all points of the compass and the teeth at the edge of the urn 

 may be depended upon to retain the spores if the conditions 

 are not suitable for their ejection. 



Such artifices as these, together with the large size of some 

 moss-capsules and the considerable number of spores which they 

 contain, mark an advance over liverwort mechanisms and the 

 moss capsular fruit, exceedingly nice in its adaptations, is the 

 most perfect and logical result of those lines of development 

 which were begun in the peat-moss capsule. The failure of the 

 moss capsular plant to achieve the highest rank is because of its 

 having lost the valuable power of indeterminate development 

 which was possessed by its horned liverwort prototype. 



Superiority of the moss-capsule over the liverwort-capsule. 

 Another point of difference between the moss capsular-plant 

 and that of the liverwort, and indicating the higher rank of the 

 former, lies in the greater development of starch-producing 

 areas in the moss. This is why the capsules of liverworts are 

 generally black while the capsules of mosses are generally green. 

 The liverwort capsule is merely a thin shell surrounding the 

 spores and the black color of the whole body is given equally 

 by the spores and their wall, but the wall of the moss-capsule 

 is like a leaf in its physiology. It consists of several layers of 

 cells, the outer portion of which functions as skin, while under- 

 neath there are areas in which leaf-green is formed. Thus the 

 moss capsular plant is not merely an elaboration of a fecundated 

 Qgg into a group of spores enclosed in a protective membrane, 

 but it is in a marked degree an independent organism. It is 

 <|uite independent so far as its assimilative power goes, and if, 



