66 



retentive than usual ; a mixture of peat and stiff loam in equal 

 proportion I have found to answer well : in the wild state it grows 

 in almost all kinds of soil, from sand and gravel to the most re- 

 tentive clay. Shade is necessary to its more luxuriant growth, but 

 it will bear exposure better than most others, especially if well sup- 

 plied with water. It may be kept in large pots, but does not like 

 confinement. 



Genus 11. PTERIS. 



GEN. CHAR. Fructification forming a continuous marginal line, 

 covered by the attenuated recurved margin of the frond. 



The fructification in this genus is very obscure in regard to its 

 primary development, and much difference of opinion has prevailed 

 among" pteridologists respecting the presence or absence of indu- 

 sium : were it one of small extent, this would be of little import- 

 ance, but the contrary is the case ; and, although the local botanist 

 can have no difficulty in recognizing our solitary indigenous species, 

 from the above superficial character, a correct understanding of 

 those points of structure that are generally adopted in the asso- 

 ciation or distinction of genera in this tribe of plants, is serviceable 

 to the general student. A close examination of the fructifying 

 frond of Pteris aquilina shows us that the lateral veins of the lobes 

 divide one, two, or three times before they reach the margin, and 

 that the extremities of the branches become anastomosed near the 

 latter, forming an intromarginal vein ; it is from this vein that the 

 thecse arise, the margin of the lobe recurving with them, not over 

 them. The thecse are not produced on the under surface, as in 

 the true dorsiferous ferns, but on the edge of the frond, the sub- 

 stance of which terminates with the vein in question, while the 

 epidermis is extended beyond it from both surfaces, and thus en- 

 closes the fructification in its earliest stage of development between 

 two membranes, the folding of which backward with their contents 

 has occasioned all the equivocality originally attaching to this part. 

 Both of the membranes have their margins ciliated with jointed 

 hairs, and under the microscope their cellular structure will be 

 found to differ in accordance with that of the upper and under 

 epidermis from which they are individually extensions. 



Pteris, Trre/w, the common Greek name for fern, signifying wing 

 or feather, well accords with the appearance of the fronds of P. aqui- 

 lina, the most common and most generally distributed of European 

 ferns. 



