O FERNS 



for perpetuating the species. In place of 

 true seeds there are substituted tiny spores, 

 contained in capsules, technically called 

 "sporangia," which grow out of the veins 

 of the leafy portion of the fronds. The so- 

 called "fruit dot" thus formed is termed a 

 sorus. It is this feature which so readily 

 distinguishes the ferns from true leaves. 



The classification of ferns depends largely 

 upon the position and variation of the sori on 

 the under sides of the full-grown fronds. 

 Another point of importance in classification, 

 although of less intrinsic value to the plant, 

 is the "indusium," the thin, membranous 

 body, more or less persistent and of various 

 forms, which covers the sorus. Thus the 

 genus dryopteris is characterised by round 

 dots and shield-shaped indusia, the exact 

 form of the latter depending largely upon 

 its point of attachment. The asplenium 

 family, on the contrary, has oblong or linear 

 fruit dots with straight or, rarely, curved 

 indusium fixed lengthwise to the upper side 

 of the fertile vein. Nature assuredly does 



