206 ELEMENTS OF SCIENCE 



prominences, each of which is called an antheridium, and 

 contains within it cells, from each of which there comes 

 forth a little spiral body bearing many cilia, by means of 

 which it can move actively about. This little corkscrew- 

 like structure is termed an antherozoid. Meantime on 

 the prothallus other prominences have appeared, each of 

 which is called an archegonium, and is a small cellular 

 tube (th'e walls of which are formed by "canal cells"), 

 open at its apex, and exposing to view a central cell 

 at the bottom of the tube. This distinct cell is 

 denominated an oosphere, or embryo cell, and remains 

 quiescent till one of the antherozoids finds its way to it 

 and blends with it. It is a process which may remind 

 us of the process of conjugation between different cells 

 of confervas and is termed impregnation. When it has 

 taken place, the embryo cell divides and subdivides till 

 it forms an incipient rhizome with its rootlet and this 

 young stem soon throws up a frond, and so the original 

 form of the fern is reproduced. 



Thus we have not only growth and change, but a cycle 

 of changes, and what is sometimes spoken of as "an 

 alternation of generations." Thus we have : 



(1) A fern-organism, which produces 



(2) A prothallus-organism, from which 



(3) A fern-organism again results. As before said, 

 nothing even faintly approximating to this cycle of 

 changes, occurs anywhere amongst bodies devoid of life. 



Let us next examine the structure and life-processes 

 of a bean plant (Vicia faba). Here we have an axial 

 organ, or stem, which is not a rhizome but grows 

 upwards from the soil, giving forth roots from its base. 

 From opposite sides of the stem spring forth foliar 

 organs, in the form of green leaves, and also branches, or 

 ramifications of the axis, which again bear green foliage 



