THE COMMON HART'S-TONGUE FERN. 165 
this netted venation being the chief peculiarity of the variety. It 
was found in Ireland in 1853 by Dr. Allehin, and is unique. 
53. viviparum (Woll). This plant is of pigmy size. The fronds 
are from one to four inches high including the stipites, and from 
half an inch to an inch and a half wide, altogether irregular in 
shape, but very conspicuously laciniate on the margin, and freely pro- 
ducing bulbille both on the fronds and stipites: indeed this variety 
affords one of the most remarkable instances of viviparous growth 
known amongst British Ferns. The fronds are sometimes more 
regular in form, but are then equally dwarf, and are also undulated 
and sinuate-lobate on the margins. The variety was found in 1853 by 
Dr. Allchin in the county of Clare, Ireland, and is perfectly constant. 
54. opacum (M.). A curious depauperated looking form, remark- 
able for its thick opaque and dull looking fronds, which are from 
three to six inches high, and narrow, but variable in width; they 
are cordate, sometimes unequal at the base, attenuate at the apex, 
irregular or sinuous and crenate or sublobate along the margin, 
sometimes contracted. It was found in Guernsey by Mr. Jackson. 
55. bullatum (M.). A dwarf plant about six inches high. The 
fronds are an inch broad, the base truncate, and slightly supralineate, 
the margin somewhat irregular, crenately or subsinuately lobate, the 
apex attenuated bluntish or forked ; they are sparingly fertile beneath, 
and bullate or blistered above, the tissue having a confused opaque ` 
appearance. The veins are irregular, sometimes netted. It was 
found at Littlehampton by Mr. Wollaston. 
This series might also include the following varieties, which are 
placed in other groups with which they accord in certain peculiarities: 
hastatum (6), marginato-fissum (61), marginato-irregulare (62), 
.coriaceum (71), turgidum (72), turgido-irregulare (78), crenato- 
crispum (99), and undulato-projectum (102). 
Marginatum Series. 
56. supralineatum (M.). The marginate group of varieties may 
be known by having an excurrent membrane developed from the 
surface of the frond. In supralineatum the membrane is confined to 
the face or upper surface. There are several forms known, some 
having but a small portion of each frond, others having one side 

