36 -Objects for the Microscope. 



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 

 microscopic 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 thecfe, 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 fit 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 (Scolopendriuin), 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 4,000 of these 

 tiny thecse, sometimes 6,000 ; and the theca? 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 



