336 DISTRIBUTION OF FERNS. PAET n. 



Islands, and one grows in matted tnfts in Kerguelen's 

 Land. In the north the Cytopteris fragilis has been 

 found in the seventieth parallel of latitude at Minto 

 Inlet, and both it and Polystichum Lonchitis have been 

 gathered at Disco, on the west side of Greenland, and 

 Aspidium fragrans on the eastern side. 



On account of the extremes of heat and cold in North 

 America there are only fifty species in all that enor- 

 mous extent of country ; while in Britain we are in- 

 debted to the humidity of our climate for a rich ve- 

 getation of thirty-six species, which adorn our wood- 

 lands, our valleys and mountains in wild profusion. 

 One-half of our ferns are also native in the Himalaya 

 mountains, where multitudes of British plants are in- 

 digenous. The fern floras of Great Britain and New 

 Zealand are the richest in species of their respective 

 latitudes, and have several species in common. The 

 ferns of Tasmania are, with few exceptions, identical 

 with those of New Zealand ; and the occurrence of the 

 rather common Australian and New Zealand Gymno- 

 gramma rutsefolia in the Pyrenees, and no where else in 

 the whole world, so far as is known, is a remarkable 

 fact in the distribution of plants.' 6 



Whatever the size of a fern may be, its spores (fig. 51 A) 

 are microscopic. They are produced within the spor- 

 angium by cell division, and are therefore free and va- 

 riously shaped. They consist of a grumous mass enclosed 

 in a double coat ; and when the spore begins to grow, 

 it sends out from the cell wall of its inner coat a white 

 tubular projection or root fibre (fig. 51 B), which passes 

 through the cell wall of its outer coat. This root 

 sucks up liquid till it expands the inner coat sufficiently 

 to burst open the outer one, and then it begins to 

 increase by the subdivision of its cells, till the primary 



6 Dr. J. D. Hooker on the ' Distribution of Ferns,' in Berkeley's ' Cryp- 

 togamic Botany.' 



