102 



Plant Life and Evolution 



The Sporophyte of the Fern a Long-lived Plant. 

 The sporophyte of the fern, unlike that of the 



~ I yg? 



FIG. 12 



Diagrams to show the possible method of evolution of the 

 sporangia of the lower ferns. 



A Section of the upper part of the sporophyte of Antho- 

 ceros, a liverwort in which the sporogenous tissue is im- 

 perfectly divided into fertile areas by the intervention of 

 sterile cells; these are unshaded in the diagram. 



B Section of the sporangiophore of a very simple fern, 

 Ophioglossum. The originally continuous sporogenous tissue 

 becomes divided into distinct masses of fertile tissue, sep- 

 arated by wide partitions of sterile tissue; each sporangium 

 opens separately. 



C Cross-section of B. 



D Sporangia of Botrychium, a fern closely related to Ophi- 

 oglossum, but having much better differentiated sporangia, 

 each opening by a transverse slit. 



mosses and liverworts, is not limited in its growth, 

 and its life does not end with the dispersal of the 

 ripe spores. It may even live for many years and 



