2 3 8 



AMPLIFICATION AND REDUCTION 



Among the Mosses the small Cleistocarpic forms are virtually dependent 

 for all their nutritive supply upon the Moss-Plant. In larger forms, such as 

 Mnium, Splachnum, and Buxbaumia, there is a well-developed assimilatory 

 system with functional stomata, and there is no doubt that it con- 

 tributes materially to the nutrition of the sporophyte. But in some cases, 

 such as Sphagnum, Ephemerum, and Nanomitrium, stomata, though present, 

 are non-functional, a fact which indicates a probability that these sporo- 

 gonia are now more dependent for nutrition upon the Moss-Plant than 

 their ancestors were. There seems some probability also that there has 

 been, in the genera last named, a reduction in the numerical spore-output. 

 These examples from the Bryophyta illustrate how the sporophyte is 

 variously dependent upon the gametophyte for nutrition ; and that while 



FIG. 116. 



Longitudinal sections through sporogonia of Cyathodium cavernarum (A), and Cyatho- 

 diumfoetidissimum (), to show their position on the thallus and their relative size. In 

 both cases the sporogonia contained spores and elaters with their walls thickened, but had 

 not quite attained their full size. ^74. (After Lang.) 



in some cases provision has been made for some degree of self-nutrition, 

 in others the dependence may have increased in the course of descent, 

 as shown by reduction of the assimilatory system of the sporophyte; and 

 there is also some indication that the spore-output has suffered by the 

 change. Thus, notwithstanding their homoporous state, it would seem 

 probable that phyletic reduction both of the vegetative system and of the 

 spore-output has been operative among them in some cases in their 

 neutral generation. 



Among the Pteridophytes the embryonic dependence is usually brief: 

 the young plant hastens to elaborate its own assimilatory system, and to 

 become physiologically independent, as in any mature Fern, or Horsetail. 

 But under some circumstances the period of dependence is liable to be 

 extended, a condition which brings with it evidences of a corresponding 

 reduction of the first-formed appendages. This is seen in certain embryos 

 borne on underground, mycorhizal prothalli, and examples of it are seen 

 in the Lycopods, and in the Ophioglossaceae. For instance, while Lyco- 



