in truth it is very evanescent.* * What, then, it may be asked, 
are the essentially distinguishing marks of the species ? As far 
as words can express them, they are very slight. The differences 
recorded by the accurate Mettenius are, “ Phegopt. Dryopteris, 
frond glabrous, ternato-pinnate or bipinnatisect; tertiary veins 
undivided or forked,”—“ Pit. Bobertiana , frond glanduloso-pu- 
bescent, bipinnatisect; tertiary veins generally forked.” The 
other characters are nearly word for word the same in both. 
No one has a more firm conviction of the two being distinct 
than Mr. Moore, for he says “ it is hardly to be supposed that 
those who have seen tolerably good examples of both would he¬ 
sitate to admit their distinctness;” and he sums up the difference 
in these w T ords :—P. Dryopteris has a loosely-spreading habit, 
while the fronds of P. Bobertianum are rigid and erect, with 
stouter stalks and ribs, and a less membranaceous texture; the 
former has ternate three-branched fronds, which is not strictly 
the case with the latter, f Of less importance, but equally or 
still more clearly available as distinguishing characteristics, are 
the perfect smoothness of P. Prgopteris, compared with the 
glandular pubescence of P. Bobertianum ,” etc. Now my very 
numerous specimens, and very good examples too, from various 
parts of Europe, Asia, and America, rather incline me to an op¬ 
posite opinion. Many of them have as strong a claim to be 
called by the one name as the other (and so they are by different 
botanists); and all those from Himalaya, of Drs. Hooker and 
Thomson, in our herbarium, which Mr. Moore refers to Pol. 
Bobertianum , I have unhesitatingly placed with P. Drgopteris: 
so that my recent very careful reconsideration of these species for 
the present work, to say the least, confirms me in the view I have 
expressed in conjunction with Dr. Arnott in the ‘ British Flora,’ 
viz. that “ we consider P. Bobertianum a very doubtful species.” 
Indeed, from most of the countries given as localities for P. Dry - 
opteris, if the specimens are numerous, some may be found ex¬ 
hibiting more or less of the characters of Bobertianum; but 
whether such are due to the presence of limestone debris, as 
seems to be the haunt of Bobertianum in this country, I cannot 
take upon me to say. I have introduced few synonyms because 
of the difficulty of settling them. 
Plate 5. Fertile plant of Polypodium Robertianum ,— vial. size. Fig. 1. 
Fertile segments, with glands and sori,— magnified. 3 . Glands and sorus,— more 
magnified. 
* On the contrary, he says in his very latest publication, ‘ English Flora,’ 
“ that the frond is smooth , except a minute downiness on the midrib.” 
f This difference I can neither see in native specimens nor in the respective 
figures of Mr. Moore, which, being Nature’s printing, cannot fail to be accurate 
in everything save the presence of the glandular pubescence of Pol. Robertianum. 
