194 Plant Life and Evolution 



for a plant of moderate size, and the mechanical, 

 or supporting tissues, which enable the terrestrial 

 plants to overcome the force of gravity, are indif- 

 ferently developed in the mosses. It has also been 

 pointed out that, having exhausted the possibilities 

 of an aquatic gametophyte, after its translation to 

 land, nature seems to have taken up the neutral 

 generation or sporophyte as a more promising sub- 

 ject for further experiments in the development of 

 a truly terrestrial plant type. The sporophyte, be- 

 ing originally an adaptation to terrestrial condi- 

 tions, seems to have a much greater potentiality for 

 development as a land plant, and once thoroughly 

 established as such, superseded the algae and mosses 

 as the prevailing type of land vegetation. The 

 ferns or Pteridophytes are the first of these typical 

 terrestrial plants. Their preeminence is due to the 

 development of true roots capable of indefinite 

 growth to correspond to the great development of 

 the rest of the plant-body, which in these plants 

 assumes a size and variety far surpassing anything 

 attained by the lower plants. The sporophyte has 

 shown itself to be extraordinarily adaptable, and has 

 been able to establish itself under very different con- 

 ditions of heat, light, and moisture. The elaborate 

 root system, with the development of very perfect 

 water conducting tissues, provides for rapid absorp- 

 tion and transport of water within the plant, and 

 the outer tissues are effectively protected against 

 undue loss of water by transpiration. 



