LIFE HISTORY OF A FERN. 239 



forms and varieties of Fern-leaves, as that would take us far beyond 

 the limits of the present paper, and though interesting from their 

 varied forms of beauty, and important as characteristics for the 

 classification and determination of genera and species, really form 

 no part of the life-history of a Fern. 



We are rather concerned now to note the mode of fructification 

 in Ferns, in which we find another wide divergence from the plan 

 which prevails in the several orders of Phanerogams, since there is 

 an entire absence of flowers and fruits in the ordinary acceptation 

 of the terms ; hence, they are included in the extensive order of 

 Cryptogams or flowerless plants. 



Taking a single pinnule from the leaf of the Maiden-hair Fern 

 for our illustration, we notice that the veins, which are distinctly 

 visible on the under-side, proceed from the mid-rib and become 

 bifurcated, a mode of division universally prevailing in Ferns. On 

 these veins are situated groups of Spore-cases, which are called 

 Sporangia. They consist of a slender stalk connecting them with 

 the substance of the leaf, and bearing a lens-shaped sac surrounded 

 by a ring or annulus of thickened cells, which are highly hygro- 

 metric in their character. These sporangia in many species are 

 covered with a thin film of cellular tissue called the Indusium, 

 affording a protection to the sporangia until they are matured. 

 These groups of sporangia are known as Sori, and their different 

 character, shape, and position are distinguishing marks in the 

 identification of species. In the majority of ferns they are dis- 

 tinct round or kidney-shaped spots, but sometimes so closely 

 situated that they become confluent, and appear to cover the 

 entire back of the leaf, and the Hart's Tongue and Bracken have 

 already been mentioned as departures from this general form. 



Within the cavity formed by the convex sides of the sporangia 

 the spores are produced by the division and sub-division of a 

 mother-cell. When these are fully matured, the indusium becomes 

 loosened around its margin ; the annulus or ring surrounding the 

 sporangium is deprived of its enclosed moisture by evaporation ; 

 and by a sudden movement, tending to straighten itself, it breaks 

 asunder, rupturing the thin side-walls, and scattering the contained 

 spores with considerable force, each with an independent existence 

 to commence another cycle of life-work. There are many varia- 



