942, ELEMENTS OF BOTANY. 
(c) The coiled spore-cases or sporangia, lying partly covered by the 
indusium. How do these sporangia discharge their spores ? 
Make a drawing, or several drawings, to bring out all these points. 
Examine some of the sporangia, dry, with a power of about 50 or 75 
diameters, and sketch. Scrape off a few sporangia, thus disengaging 
some spores, mount the latter in water, examine with a power of about 
200 diameters, and draw. 
302. Life History of the Fern. — When a fern-spore is Sown on 
damp earth it gradually develops into a minute, flattish object, called a 
prothallium, Fig. 208. It is a rather tedious process to grow prothallia 
from spores, and the easiest way to get them for study is to look for them 
on the earth or on the damp outer surface of the flower-pots in which 
ferns are growing in a greenhouse. All stages of germination may 
readily be found in such localities. 
Any prothallia thus obtained for study may be freed from particles of 
earth by being washed, while held in very small forceps, in a gentle 
stream of water from a wash-bottle. The student should then mount 
the prothallium, bottom up, in water in a shallow cell, cover with a large 
cover-glass, and examine with the lowest power of the microscope. Note: 
(a) The abundant root-hairs, springing from the lower surface of the 
prothallium. 
(6) The variable thickness of the prothallium, near the edge consisting 
of only one layer of cells. 
(c) (In some mature specimens) the young fern growing from the 
prothallium, as shown in Fig. 208, B. 
The student can hardly make out for himself, without much expendi- 
ture of time, the structure of the antheridia and the archegonia, by the 
cooperation of which fertilization takes place on much the same plan as 
that already described in the case of mosses. The fertilized odsphere of 
the archegonium gives rise to the young fern, which grows at first at the 
expense of the parent prothallium but soon develops roots of its own and 
leads an independent existence. 
The mature fern makes its living, as flowering plants do, by absorption 
of nutritive matter from the soil and from the air, and its abundant 
' chlorophyll makes it easy for the plant to decompose the supplies of 
carbonic acid gas which it takes in through its stomata. 
generally accessible form, but has no indusium. Pteris aquilina is of world-wide 
distribution, but differs in habit from most of our ferns. The teacher who wishes to 
go into detail in regard to the gross anatomy or the histology of ferns as exemplified 
in Pteris will find a careful study of it in Huxley and Martin’s Biology, or a fully 
illustrated account in Sedgwick and Wilson’s Biology. 
