372 ON REPRODUCTION. 
species (see page 37). Although these spores are so small 
they are nevertheless endowed with an extraordinary 
power of retaining their vitality ; and, being easily wafted 
by currents of air, readily account for the wide geogra- 
phical range of some species of Ferns. When naturally 
or artifically placed under favourable conditions they burst, 
and expanding in the form of a simple oblong cell, on 
which other cells are successively developed, ultimately 
form a thin green membrane called the prothalliwn, 
which, when arrived at full size, is of a reniform cordate 
shape, or sometimes bilobed, or obcordate, varying from 
about i to 3 inch in diameter, and adhering to the surface 
on which it vegetates, it has much the appearance of a 
small foliaceous lichen or Marchantia. In time a small 
bud makes its appearance near the base of the prothal- 
lium, which increases in size, and ultimately a small frond 
is produced, which is succeeded by others minim 
larger, thus becoming a plant. 
The increase of the prothallium and sprouting of the bud 
` is readily seen by the naked eye, and the cultivator is 
satisfied with the result; but he finds himself often dis- 2 v 
appointed, for after having obtained abundance of prothallia 
from many different species, they nevertheless do not ae 
always produce a bud germ. This is now supposed to be — 
explained by the discovery made in 1848 by Count Suminski, 
a Polish botanist, that Ferns possessed organs analogous - e 
. to the stamens and pistils of flowering plants, and that - < 
_ these were produced on the under side of the prothalium; ` ` = 
. they are represented by two kinds of cells, one called E 
 Antheridia and the other Archegonia. The first (of which ` 
there are generally between 30 and 40) consist of round ` 
cells, which contain vermicular spermatozoids that issue - 
from the cells when arrived at maturity. The cells of the : 
