82 



ELEMENTARY STUDIES IN BOTANY 



investing a mass of spore-producing cells (Fig. 66, A). 

 There is no stalk, and there are no sterile cells except the 

 single layer forming the jacket. When the sporophyte 

 gets to be very complex, it is important to remember that the 

 oldest tissue in it (historically) is that which produces spores 

 (sporogenous tissue), for this will clear up many false im- 

 pressions. 



Progressive changes. The conspicuous change observed 

 in certain other Liverworts is that the cells inclosed by the 

 sterile jacket do not all produce spores. For example, in 



some forms one-half of 

 the inclosed tissue pro- 

 duces spores and the 

 other half remains sterile 

 (Fig. 66, B). This sterile 

 tissue forms a short stalk, 

 and so different regions of 

 the body begin. 



In other forms, still 

 more tissue remains ster- 

 ile, which means that the 

 sporogenous tissue be- 

 comes relatively less in 



amount (Fig. 66, C). With the increase of sterile tissue, the 

 stalk and the capsule become more complex (Fig. 66, D) ; 

 until in the higher Mosses almost the whole complex sporo- 

 phyte is sterile, and the sporogenous tissue is not only 

 relatively small in amount, but appears late in the develop- 

 ment of the sporophyte (Fig. 66, E). The sporogenous 

 tissue which in the beginning was the first and only tissue 

 (except the sterile jacket), becomes finally in the higher 

 Bryophytes the latest and most inconspicuous part of the 

 sporophyte. ' It is the ever increasing sterile tissue that the 

 higher plants use in carrying the sporophyte to still more 

 advanced stages. 



FIG. 65. Spore-cases of a moss from which 

 the lids have fallen, showing the teeth. 

 After KERNER. 



