FERNS AND THEIR RELATIVES 79 
features, but upon every little detail, that we can face 
the harder problems of the causes that have brought 
these results to pass, and the principle upon which they 
have worked. Remember also that when one talks of 
a “law of nature,’ this law is not a rule that never 
should, and never can, be broken, but merely an in- 
telligent summary of a series of hitherto observed facts. 
It is from observed facts that botanists have drawn their 
theories as to the close relationship of all plant-life, and 
the fern group is an excellent illustration. Upon the one 
hand the tree-ferns, by their structure and growth, lead 
us on to the pines and firs of the flowering plants; upon 
the other the filmy ferns, with their thin and humble 
leaves, lead us back tio the mosses. 
Again, whilst the appearance of the fibro-vascular 
bundles warns us that we are approaching the highest 
forms, there is the backward link of the “alternation 
of generations” which is, though in a different way, as 
marked a feature among the ferns as among the mosses. 
You will remember that the ordinary moss plant was the 
generation provided with two different kinds of cells for 
reproduction, known as antheridia and archegonia, or male 
and female cells. The fertilised archegonium, to which 
the snake-like morsel of protoplasm from the antheridium 
had joined itself, became the “ moss-fruit,” which, though 
never obtaining a wholly separate life, had yet in some 
sort an existence of its own, independent of the plant. 
You will remember how the spores from this short-lived 
“moss-fruit,” if falling on suitable soil, finally sent up 
again the branching, conspicuous moss plant, with its 
sexual organs. Amongst the ferns we still have alterna- 
tion. The father, so to speak, is not in the least like the 
son, but the grandson is an exact reproduction of the 
