312 



THE MICROSCOPE. 



buds like other plants, but that their leaves, or fronds as 

 they are properly called, when they first appear, are rolled 

 up in a circinate form, and gradually unfold, as in fig. 1 68. 



Fig. 168. Male Fern. A portion of leat with sori. 



Ferns have no visible flowers; and their seeds are produced 

 in clusters, called sori, on the backs of the leaves. Each 

 sorus contains numerous thecse, and each theca encloses 

 almost innumerable sporanges, with spores or seeds. 

 There are numerous kinds of ferns, all remarkable for some 

 interesting peculiarity ; but it is their spores which are 

 chiefly sought for by the microscopist. 



The first account of the true mode of development of 

 Ferns from their spores was published in 1844, by Nageli, 

 in a memoir entitled Moving Spiral Filaments (spermatic 

 filaments) in Ferns, wherein he announced the existence of 

 the bodies now called antheridia; but, mistaking the 

 archegonia for modified forms of the antheridia, he was 

 led away from a minute investigation of them. If lie had 

 followed the development of the prothallia further, he 

 would have detected the relations of the nascent embryo, 

 which would probably have put him on the right track. 

 As it was, the remarkable discovery of the moving spiral 

 filaments occupied all his attention, and caused him to fall 



