THE SOFT PRICKLY SHIELD FERN. 143 
instances in which it has been observed, having been on potted 
plants. We think it may be the combined result of the check 
caused by the cramping of the roots incidental to pot-culture, and 
the excitement arising from the very moist atmosphere which is kept 
up in most Fern-houses. The instances thus observed, however 
produced, appear to afford additional evidence that the fronds of 
Ferns are not leaves, as some would call them, to which, however, 
the fact of their normally bearing the fructification seems repugnant ; 
but that they atleast include something of the nature of branches. 
Another fact may be mentioned as militating against the opinion . 
that the fronds of Ferns are mere leaves. Leaves, it is maintained 
by physiological botanists, have their points first formed, the per- 
fected apex being as it were pushed forward by accretion from below. 
Now in the fronds of Ferns, it may often be seen to demonstra- 
tion, that the lower parts are perfectly developed and bear mature 
sori, whilst the apex is still unrolling ; this is very obvious in the 
genus Nephrolepis. Besides the bulbilliform mode of increase above 
adverted to, Mr. Wollaston has observed a different kind of what is 
supposed to be viviparous development in the Polypodium vulgare 
var. omnilacerum, on a plant communicated by Mr. E. T. Bennett. 
In this case, the development consisted of prothalloid growths, on 
the apices of the serratures of the lobes; these had every indication 
of being capable of further evolution, though unfortunately the 
frond was broken off before they were observed, so that their vital 
energy could not be fully tested. 
Polystichum angulare is one of those Ferns which exhibit a very 
large degree of variation, the differences in some instances being 
very marked. There are several distinct modes of variation. The 
blunt-pinnuled broad-fronded form is taken as the type. Diverging 
from this, some forms have the fronds small and extremely narrow ; 
others have the pinnules narrow and acute; while in some they 
are very densely placed, and in others they are distant. One 
remarkable form has the pinnules nearly round and entire. Some 
have the secondary rachides distinctly winged, and uniting the bases 
of the pinnules into a confluent mass, thus obscuring one of the 
essential characteristics of the species—the stalked pinnules. A 

