THE EVOLUTION OF THE SPOROPHYTE. 



17 



complex structure as is found in most of the Angiosperms, or 

 typical flowering plants. The latter represent the highest 

 plant type, and the sporophyte exhibits almost endless variety, 

 especially in the flowers. The gametophyte, however, is 

 reduced to a microscopically small body consisting of a few 

 cells only. 



The type of structure exhibited by the Angiosperms has been 

 remarkably successful, and the great bulk of existing terrestrial 

 plants are Angiosperms, which have to a great extent replaced 

 the ferns and Gymnosperms of earlier geologic times. In the 

 water, however, where conditions have changed less, the lower 

 types of plants still persist, and the Angiosperms are much less 

 important. 



Summary. 



In passing from the higher algae and lower liverworts to the 

 ferns and flowering plants, it is the sporophyte, or non-sexual 

 plant, which continues to increase in importance. Starting as a 

 minute globular capsule completely filled with spores, there is 

 first a sterilization of a part of the tissue which becomes devoted 

 to the vegetative needs of the sporophyte. There is soon 

 developed a special absorbent organ, the foot, and later a sys- 

 tem of green tissue for the assimilation of COg. The sporo- 

 phyte at last, in the ferns, by the development of a root, 

 becomes entirely self-supporting, and from this time the sporo- 

 phyte becomes the important phase in the plant's existence, the 

 gametophyte becoming more and more reduced. The complete 

 independence of the sporophyte is associated with the develop- 

 ment of special organs, — and a corresponding perfecting of the 

 tissues. 



The sporogenous tissue, which at first constitutes practically 

 the whole of the sporophyte, finally becomes restricted to spe- 

 cial organs, sporangia, which are met with in all the higher 

 plants. The development of the spores themselves, however, 

 is extraordinarily uniform throughout, and is one of the strongest 

 arguments for the common origin of all these forms. 



The remarkable development of the sporophyte in the higher 

 plants has been influenced by many factors, but probably the 



