568 MOSSES AND FERNS CHAP. 



The foot is an absorbent organ of great efficiency, and through 

 it the growing embryo is nourished at the expense of the 

 gametophyte, upon which the embryo lives much as a parasitic 

 Fungus does upon its host. This development of a special 

 absorbent organ at once allows a longer period of growth for 

 the embryo, and a correspondingly greater development of spo- 

 rogenous tissue. 



The next evidence of progressive sterilisation in the tissues 

 of the sporophyte is the development of an intermediate region, 

 the seta, and the sterilisation of some of the sporogenous tissue 

 to form elaters. Both of these developments, however, are 

 concerned solely with the dissemination of the spores. In the 

 more advanced sporophytes of most Liverworts, the cells 

 develop more or less chlorophyll, and to this extent the sporo- 

 phyte is capable of self-support. The sporophyte, however, 

 remains dependent to a great extent upon the gametophyte, 

 from which, by means of the massive foot, it receives most of 

 its nourishment. 



The first marked evidences of a capacity for independent 

 existence in the sporophyte are found among the Anthocerotes 

 and the Mosses. In these classes, the sterilisation of the spo- 

 rogenous tissue is carried much further than in any of the 

 Hepaticse, and much the greater part of the sporophyte is com- 

 posed of sterile tissue. In such forms as Anthoceros and 

 Funaria, the sporogenous tissue forms but a small fraction of 

 the whole sporophyte, which grows for several months and 

 develops an extensive and efficient system of tissues for photo- 

 synthesis. Conducting tissues are also present, and in the 

 Mosses the seta and capsule have conspicuous mechanical tissues 

 as well. The sporophyte, nevertheless, receives its water sup- 

 ply from the gametophyte through the foot, as it does in the 

 Liverworts. 



With the establishment of a true root putting the sporophyte 

 into direct communication with the earth, the independence of 

 the sporophyte is completed. Whether the direct contact with 

 the earth acted as a stimulus to vegetative activity, as it seems 

 to have done in the case of the transference of the gametophyte 

 from water to land, of course we can only conjecture ; but the 

 extraordinary complexity of the sporophyte which is found in 

 all Pteridophytes indicates that this is not improbable. With 

 the establishment of the sporophyte as an independent, typically 



