360 FERNS. 



with a number of round spots called sori, very con- 

 spicuous from their golden yellow or rich brown hue. 

 Examination with a powerful lens reveals that each 

 of these spots is a group of tiny globules, known as 

 thecce, each elevated on a slender stalk, and closely 

 crowded. A microscope is, however, needed to discern 

 more. 



By the aid of this instrument we perceive that each 

 theca is a hollow sac, strengthened by a stout ring, 

 marked by transverse bars, that passes vertically round 

 it, like the brass meridian round a globe. At a cer- 

 tain period this elastic ring bursts, rupturing the walls 

 of the theca, and scattering its contents, viz., the spores, 

 which are the ultimate agents of reproduction, answer- 

 ing to seeds. They are, however, homogeneous cor- 

 puscles, generally of an ovate or rounded form, with 

 three more or less prominent ridges running along 

 them longitudinally. 



Under the influence of warmth and moisture, the 

 thick but brittle outer coat of the spore bursts, and 

 the contents protrude as a clear bladder, which by 

 growing assumes a tubular form, divided by transverse 

 partitions ; in other words, it is a single linear series 

 of oblong cells, within which, on the inner surface of 

 their walls, grains of green substance, (chlorophyll,) 

 the colouring matter of plants, develop themselves. 

 At the same time, a slender root grows out from the 

 lowest cell. After the conferva-like filament has 

 made its fourth or fifth linear cell, the terminal one 

 divides longitudinally, so that two oblong cells placed 



