'BOTANY. 93 
Each sorus, when magnified, is seen to consist of numerous 
capsules (thecæ); these capsules contain the spores. The 
spores are angular-shaped bodies (Fig. 125, a), with an 
external coat of a brownish color, which is variously marked, 
like the pollen of higher plants. The spores, when placed 
in a damp surface and exposed to the proper influences of 
heat and light, germinate; that is, the angles of the spore 
are rounded off, the internal coat of the spore is then pro- 
truded, becoming the root-fibre (Fig. 125, 6); the outer coat 
of the spore bursting, the inner coat grows in an opposite 
direction to that of the root-fibre as an elongated filament 
(Fig. 125, c); cell after cell is added in a longitudinal 
direction, the plant soon resembling an Alga. After a 
time, however, the cells are produced transversely as well 
as longitudinally, resulting in the formation of a flattened 
leaf-like expansion (Fig. 125, 7), a cellular structure, the 
so-called Prothallus, which can scarcely be distinguished 
from a young Marchantia. In this Prothallus are developed 
Archegonia and Antheridia: the union of the embryo-cell 
of the Archegonia and the spiral filament of the Antheridia 
gives rise to the new Fern, which may be seen growing 
out of the Prothallus (Fig. 126), which soon passes away. 
These two stages in the life of a Fern represent two distinct 
plants. The Prothallus stage is a cellular plant closely 
resembling a young Marchantia, which is later transformed 
into a stem- and leafbearing plant. The growth of the 
Horse-tail offers the same metamorphosis; spores pro- 
ducing a Prothallus from which the Horse-tail is developed. 
While the Mosses are probably the posterity of Junger- 
mannia-like plants, the Ferns have most likely descended 
from forms allied to Marchantia; this view being based 
on the fact of the Fern passing through a Marchantia-like 
stage, with similar reproductive organs. 
