Pol ystichum. 
147 
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 at least 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 perfected apex being, as it were, pushed forward by accretion from below. Now, in the 
fronds of ferns it may often be seen to demonstration 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 vidgare 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.” * 
* “Nature-printed British Ferns” (8vo edition), vol. i., pp. 142-3. 
