472 THK FERN FAMILY. 



root do not all produce sori necessarily ; sterile fronds and fertile ones 

 are almost always intermingled. The sori are in perfection about the 

 close of summer, and last till the end of autumn, and in the evergreen 

 species even till spring. When examined with the microscope, they 

 are found to consist of multitudes of little spore-boxes, termed thecce. 

 Every " theca " is usually girt with an elastic ring, which seeks to 

 straighten itself when the spores are ripe, and thus tears open the 

 theca, and disperses them. The spores are exceedingly minute, and 

 produced in incalculable quantities, the little spangles, like the " fairies' 

 money" the poet has aptly likened them to, literally " turning to dust." 

 While young, the sori are covered by a very delicate membranous lid, 

 called the " tndusium," which cracks or detaches itself, in the different 

 genera, in many different ways, and furnishes excellent discriminating 

 marks for them. Some ferns, instead of having their sori on the 

 under surface of the frond, bear them in terminal panicles, as repre- 

 sented in Fig. 206, while in others they are packed into a kind of 

 spike, and in others again protruded from the edge of the frond in the 

 shape of little baskets or cornucopias. In these latter kinds the elastic 

 band round the theca is generally imperfect, or altogether wanting. 



The number of species of ferns is estimated at two thousand. They 

 grow in all parts of the world, loving chiefly moist Avarm woods upon 

 islands in happy climates, though some prefer the open plain, and 

 even walls. Not a few haunt the edges of waterfalls, and shady 

 cavernous rocks in deep dells and quiet glens, while others seat them- 

 selves on wild cliffs by the spray of the sea. It is a peculiar allure- 

 ment to the study of this beautiful tribe, that their habitats are almost 

 always of this romantic and elfin character. 



The British ferns, like the grasses, are variously reckoned, different 

 authors making them thirty-six, forty-two, and fifty, according to the 

 value they severally attach to the distinctive characters. Forty may 

 be taken as the likeliest number, Manchester having twenty-two of 

 them. They form an admirable subject for the young botanist to 

 commence with, the extent being small, specimens easily procurable, 

 and no plants so easy of preservation for the herbarium. It is im- 

 portant to observe that the fructification must be examined while it is 

 youriff. The sori are then distinct, and the indusia perfect ; whereas, 

 when mature, the former often become " confluent," or commingled 

 at the margins, so that instead of clear outlines, we have nothing but 

 confused and dusty patches. The indusia at the same time shrivel up, 

 and either fall off or are concealed by the flood of thecaj. 



