THE PTERIDOPHYTES 143 



it " catch the eye," and 'it .could hardly be noticed by 

 any but a trained observer. The gametophyte of a 

 Moss endures, even after it has formed the sporophyte, 

 and the latter has done its work and decayed ; but this 

 is not so with the Pteridophytes. In their case the 

 prothallus, after the fertilization of the ovum, and the 

 launching of the sporophyte on its career, disappears. 

 The sporophyte becomes independent at an early stage ; 

 it can " do for itself," for it has leaves, stems and true 

 roots, and all the machinery essential for honest inde- 

 pendence. But it lives for posterity as well as for itself, 

 for it produces the spores from which new generations 

 arise. These spores are borne in organs, known as 

 sporangia, which occur on the leaves, or in close relation 

 to them. 



In the plants to be discussed in this chapter we must, 

 on the understanding just arrived at, remember that it 

 is the asexual sporophyte that attracts our attention in 

 Nature ; it is a highly organized plant, having true roots 

 instead of mere rhizoids, as in the Mosses, and whereas 

 in the latter we detect a mere trace of conducting tissue, 

 in all the Pteridophytes this tissue is always present, and 

 is elaborated into a vascular system which traverses 

 stem, leaves, and roots. And, be it noted, the leaves 

 are as advanced in structure as those of the average 

 flowering plant. 



The majority of the Pteridophytes produce spores 

 that are all alike, and from these, when they germinate, 

 prothalli arise bearing both male and female organs; 

 but there are cases in which the sexes are represented 

 on different prothalli. In some instances two sizes of 

 spores are produced, in which event the larger (mega- 



