VIU 
European Ferns. 
observe, either from its small size or from becoming torn and withered, or being concealed by 
the numerous full-grown sporangia. It is quite necessary always carefully to examine into this 
point. In the case of the covering found in several marginal sori, in which the edge of the 
frond is turned back and partially covers the sporangia, it is not always easy to say whether 
there is an indusium present or not. Thus, in the Parsley Fern we have the reflexed portion 
of the edge of the frond scarcely altered at all, whilst in Pteris cretica, Adiantum, and other 
ferns, there is a distinct membrane extending from the margin, and more or less covering 
the line of sori. In the uncertainty as to the true nature of this organ it is convenient to call 
it a false indusium. Our common Bracken shows, besides this false indusium, a true indusium 
also, which is situated beneath the sori. And this leads us to notice that the indusium may 
be either inferior — i.e., forming a cup or a scale below the sporangia — or (more usually) superior, 
when it covers them. Examples of the former kind are seen in the Ostrich Fern, and very 
beautifully in the little Woodsias ; also in the species of Cystopteris and in the Filmy Ferns, all 
of which kinds present differences which are fully described in the succeeding pages. The 
superior indusia present less variety. They form, when young, a complete investment over 
the sporangia, but as the latter become ripe the indusium becomes detached at its edge. 
Their attachment is generally to the receptacle, either by their centre to its summit or at the 
side. 
Mode of Reproduction. — We have seen that the spores are liberated from the sporangia 
when ripe by the rupture of the latter ; we have now to examine in what way the new fern 
has its origin. When the spores fall in a suitable damp place, they, usually after some little 
period, germinate. But their germination is quite unlike that of a seed ; there is no young 
embryo plant in the spore, and no putting forth and unfolding of a delicate root and little 
fronds belonging to a young fern. A plant is produced, to be sure, but it is wholly unlike 
the parent. The germination of fern spores can readily be watched in any hot-house, and 
what is seen as the result is a very small, flat, membranous green body, which is attached 
to the soil by several delicate rootlets. Its outline varies, but is usually more or less circular 
or kidney-shaped ; its transparent, clear, green, and cellular texture gives it a great similarity 
to the little plants called Liverworts. To this structure the name prothallium is given. 
Though so delicate a structure, it is not always an evanescent one, and may even last several 
years. 
The prothallium seems to have been first clearly seen by Dr. Lindsay, whose observations 
are recorded in the “Transactions of the Linnean Society” for 1792 (vol. ii., p. 93). He well 
figures the commencement of the new fern, but it was not for many years after that the 
mode in which it originated from the prothallium was understood. It was in the year 1844 
that the mystery was cleared up by the discovery of the reproductive organs — which everybody 
had hitherto looked for upon the mature fern — on the minute prothallium. These organs are 
necessarily of two kinds, and may be roughly considered to be analogous to the stamens and 
pistils of flowering plants. They are, of course, very minute, and require the microscope for 
their examination, and are termed antheridia and archegonia. In the great majority of cases 
both kinds are found on the same prothallium ; their usual position is on the under-surface, 
the antheridia among the rootlets at one end, and the archegonia in the kidney-shaped 
prothallia, just behind the indented portion. The antheridia arc minute cellular sacks, which 
burst, when mature, to liberate a number of microscopic, spirally-twisted, ciliated bodies 
endowed with movement, and called spermatozoids. The archegonia are larger and bottle- 
shaped, with a rather long neck, and contain at the base a minute central cell, which is the 
