THE FERN BULLETIN 



67 



In the mosses, however, the gametophyte — that part 

 which corresponds to the prothallium of ferns — does 

 practically all the work of food-getting and supports 

 the spore-bearing generation — which is equivalent to 

 the ordinary fern-plant — throughout its existence 



Our ferns, of course, are self-supporting except foil 

 a brief period in infancy when they are dependent upon 

 the gametophyte exactly as the spore-bearing parts of 

 the moss are for life. It will thus be seen that the 

 office of bearing spores was selected for the fern plant 

 long before it needed to secure its own living and the 

 first step toward an independent existence was un- 

 doubtedly made by turning part of the spore-bearing 

 tissue into a green blade for vegetative functions. Some 

 of our simplest fern-worts still point to the way in 

 which fern fronds were evolved by being little more 

 than a cluster of spore-capsules with some rudimentary 

 green leaf-like parts. 



Thus it may be seen that when a fern frond that is 

 normally fertile becomes sterile, it has but followed a 

 precedent set for it since time began for the ferns, 

 while a sterile part that becomes fertile is the only one 

 that may be said to revert to a former condition, 

 though curiously enough, we customarily refer to fer- 

 tile parts becoming sterile as true cases of reversion. 



Just how late in the history of any given frond it 

 is able to change from fertile to sterile or vice versa 

 does not seem to be very definitely known. Probably 

 the power to make the change exists until the cells 

 have nearly ceased to multiply. Ferns belong to a class 

 which the old botanists knew as Acrogens, or tip- 

 growers from the fact that the region where new cells 

 are produced is at the apex. As a consequence of this 

 method of growth, the basal parts of fern fronds are 



