82 TYPES OF BRITISH PLANTS 
in the swollen part, and the new spore-bearing generation 
starts. 
After a short rest, the original cell splits into several. 
One of them drives its way into the prothallium, and 
from it sucks up nourishment—one forms the root into the 
earth, another the stem, and a fourth the first frond. The 
work of the prothallium is now done, and when the new 
fern is established in life, its green frond putting the 
chlorophyll machinery in action, and its root getting food 
from the earth, the prothallium, the sexual generation, 
dies away. The young bracken stem runs prostrate along 
the ground, sending up frond after frond as it pushes its 
way along, and flourishing exceedingly. The next necessity 
is to secure the production of new prothallia, and for this 
we must have spores. Upon the back of some of the 
fronds, not usually of all, are developed the spore-cases— 
sreen at first, but turning brown as they ripen. In the 
Bracken, the cases, or sporangia, are grouped along the 
edges of the fronds, and the margin folds back, so as to 
protect them until the time comes for their dispersal. 
Then the leaf flattens, and the spore-cases split, allowing 
the wind to carry the contents where it will. Once 
more prothallia are formed, and the process we have 
traced begins afresh. 
Now, this life history is true, generally speaking, of all 
ferns. Each goes through the two stages of existence, 
and in its more conspicuous stage bears spores upon 
some or all of its fronds.) We have next to consider 
how to know the different groups to which ferns belong, 
and this is decided by certain details as to the arrange- 
ment and method of protection of the spores. The 
spore-cases, in the first place, may be grouped on the 
edges of the fronds, or along the veins, or, sometimes, 
