ONOCLEA SENSIBILIS.—SENSITIVE FERN. 19 
familiar plants, have propagated themselves unchanged for half 
a million years?” It is impossible to look on this beautiful fern 
without a species of veneration for its wonderful antiquity. 
Some have thought, however, that it shows some disposition to 
change, and have named one supposed variation— O. od/usilobata. 
But even this has been ascertained in modern times to be only a 
phase of development in the transformation of the frond to the 
reproductive condition, for the mass of fruit (Fig. 3) is nothing 
but the frond (Fig. 2) in a very much changed state. If we take 
any fern, say the common Polypody, we shall see that the first 
leaves are barren, that is, have no fruit dots on their under sur- 
faces, while others are completely covered with sori or fruit dots. 
Still there is a general resemblance between the fertile fronds 
and the fronds with sori on them. But in the case of our sensi- 
tive fern, the portions of the frond on which the fruit dots are 
placed have rolled backwards and completely enveloped the 
mass of sori, giving to this fruiting “frond” the appearance of 
a cluster of “berries,” as Dr. Darlington expresses it. Now, the 
variety obtusilobata is simply a frond in an imperfectly developed 
fertile condition. There are fewer sori on the frond than in the 
form we generally see, and the lobes do not recurve very much, 
but retain a good portion of the regular frondose condition. 
This form is not unfrequently met with, and is very welcome to 
the young student as giving the key to the structure of the more 
advanced fruiting frond. 
The manner in which this fertile frond succeeds the barren one 
will be found particularly interesting to the close observer. Fig. 
4 is a portion of the rhizoma or underground stem taken in early 
_winter. The first leaves of the season come out in a nearly 
simultaneous pair, Figs. 5, 5, and seem attached to the side of 
the rhizoma like a pair of grasshopper legs. After this effort 
others are produced which never reach a condition beyond long, 
slender scales, Figs. 7, 7. About the middle of summer another 
single one is formed which becomes the fertile “frond,” Fig. 3, 
and which proceeded from Fig. 6. Then a few more scales are 
