2 | ON GENERA AND SPECIES. 
They vary considerably in size, many not being larger 
than mosses and liverworts and of as delicate a texture; a 
very few partake of the character of shrubs, and about one 
hundred and fifty assume the aspect of trees, some attain- 
ing the height of fifty or more feet. 3 
As the special character of their structure is fully ex- — 
plained further on, the above is sufficient to give an idea of ` 
the nature of Ferns, 1 
Although Ferns possess but few economic properties, 1 
either as food, medicine, or in the arts, they have never- - 
theless become of great interest to botanists, their study - 
being termed Pieridology, on which many books have been ` 
written, and during the last fifty years have also como into 1 
special favour with amateur plant cultivators, and lovers of | 
pretty plants. The constant desire for novelty has led 3 
both public and private plant collectors and persons living — 
in foreign countries to devote special attention to the col- 
lecting of Ferns, both for herbarium specimens and also as 
living plants. By these means the collections of Europe 
. have become greatly enriched. It is recorded that the 
. Royal Herbarium at Kew contains 50,000 specimens of 
Ferns, which have been communicated by no less than 
about 150 public, private, and trade collectors from all 
regions: the Fern collection in the herbarium of the 
British Museum is also very extensive. "These, with the 
living collection at Kew, which in 1864 contained above 
one thousand species, have afforded ample means for study 
and determining the genera and species of Ferns. Many 
extensive living collections are also formed by amateurs, 
who in rivalry enhance their value to such an extent that 
95 much as fifty guineas is frequently given for a single 
plant of fashionable repute at the time. Ha 
Of late years many books have been published on Fern: 
