SPORE-CASES OF FERN. 39 



There are upwards of forty genera and a thousand species 

 of moss, of which 39 genera and 400 species are found in 

 Great Britain. 



SPORE-CASES OF FERN. 



The fructification of ferns affords a great variety of micro- 

 scopic objects, though we rarely find any but the spore-cases 

 of the common Polypodium mounted in this way ; therefore, 

 after looking at the slide, we should by all means collect 

 and examine as many varieties of fern as we can, not only 

 for the shape of the thecse, as these little cases are called, 

 but for their position on the frond. 



This Polypodium is a most common fern, growing upon 

 old walls and hedgerows, and the round yellow spots on 

 the underside of the frond are masses of these spore- cases 

 called sori. 



Observe that each theca is clasped by an elastic ring or 

 band, called the annulus, and the spores are kept safely 

 during their growth, as in a golden casket ; but, as soon as 

 they are tit for dispersion, the membrane which encloses 

 them breaks, and the elastic band is seen with an empty 

 little cup at each end. The spores themselves resemble 

 pollen-grains, and are very prettily marked ; but will require 

 a higher power, and had better be examined from a fresh 

 frond, with a drop of water, or a drop of oil of lemon, 

 which is an excellent assistant in the observation of pollen 

 and spores of all kinds. 



The great profusion of these organs of reproduction is 

 astonishing. If we take a leaf or frond of the common 

 Hart's-tongue (Scolopendrium) , and count those brown 

 lines on the underside, which are the sori, we find at least 

 fifty in a good-sized frond; in each sorus 4000 of these 

 tiny thecse, sometimes 6000; and the thecse themselves 

 enclose about fifty spores : thus we shall find that a single 

 leaf of the plant may give rise to no fewer than ten millions 

 of young ferns. 



An interesting experiment may be made to learn the 

 growth of a fern, by simply shaking some ripe spores on 

 a saucerful of fine mould, covering it with a bell-glass or 



