PREFACE. 
XIX 
known, would justify their separation into species, if not 
genera. No more striking illustration of this remark could 
be given than our (f. 9) representing Scolopendrium vulgare, 
ramo-marginatum of Clapham, the sori of which form an 
interrupted edging to the lamina, an arrangement at right 
angles to the usual direction of the fruit, as well as to its 
relation to the veins of the frond ! 
7. Besides changes incidental to the several parts of a 
Fern, there are yet other sources of variation, of which the 
only one noteworthy is change of Colour. Of this we have 
few native examples, chiefly observed in the common Poly- 
pody variegatum, N.F.,p. 58, and in the Hart’s-Tongue, N.F., 
f. 695, 739, &c. ; but in exotic species, a highly ornamental 
feature is given to a stove by the deep crimson tints of 
the expanding fronds of Adiantum Farleyense and other 
Adianta, and especially by the chequered aspect of Pteris 
tricolor ; a plant of which, cultivated by a lady in a wide 
glass cylinder with a movable cover, presented the richest 
and most lovely sight. 
Into the causes of the many variations in development 
to which Ferns are liable, whether in the wild or culti- 
vated state, we cannot fully enter. 
The exposure of the plants to a dry impoverishing con- 
dition, the pressure of rocky masses upon the roots, their 
stimulus by a free and rich soil, attended by a warm humid 
atmosphere ; or, again, the effects of excessive moisture 
about the roots, or of mineral and other solutions in the 
soil, prove, in turn, fruitful causes of increase or defect in the 
several parts of Ferns : but we owe to cultivation far more 
numerous varieties, perhaps, than to any other cause. 
The occurrence of short copiously branched plants of the 
Moon wort Fern, at Osmaston Manor, and on Harlow Moor, 
near Harrogate, appeared to be the result of a check given 
to the descent of the roots by fragments of stone or pebbles : 
while the stations of Lastrea Fsenisecii, both in England 
Wales, and Ireland, upon wet stony soil, would account for 
