FILICINEM. 
markable, finding its parallel only among the Ophioglossaceae. In old plants of 
Pteris aquilina the formation of the leaf commences fully two years before its un- 
folding : — at the commencement of the second year only the leaf-stalk is as yet 
in existence, about one inch high. Up to this period its growth has been effected 
by a single apical cell which is divided by oblique walls in alternating directions ; 
it is now carried on by a number of marginal cells which divide. The pinnae are 
derived from the segments of the single apical cell ; the veins are formed by the 
repeated divisions of the marginal cells (Sadebeck). In the summer of the second 
year the lamina arises for the first time at the apex of this rod-like body, and may be 
found hidden in the form of a minute disc beneath the long hairs. It immediately 
bends downwards at its apex, and hangs down like an apron from the apex of 
the stalk (Fig. 301, B, C, Z)). Its growth now proceeds underground, so that it 
does not begin to unfold till the third spring, when it is raised above ground 
by the elongation of the leaf-stalk. The whole of the leaves of a rosette of Aspidiwn 
Fig. -^01.— Pteris aquilitia; A the end of a stem st, the apex lying at ss ; by its side at b is the rudiment of a leaf, 
bs the stalk of a leaf in the second year, at h its lamina enveloped by hairs, K a bud at the back of the leaf-stalk, 
w roots ; B a young leaf in the second year, bs its stalk, I its small lamina with the hairs remov ed ; C longitudinal section 
of a similar leaf, connected with the* transverse section of the stem st, bs and I, as in B ; D the lamina of a leaf in the 
second year seen in front, i. e. on the upper side (X about 5) ; the first segments have begun to be formed ; E horizontal 
longitudinal section of a branching of the stem, ss s's the two apices, a a brown epidermal tissue, b b brown sclerenchyma, 
g fibro-vascular bundles. {A, B, C natural si2e.) 
Filix-mas have been in course of formation two years before their unfolding; 
the leaf-stalk is in this case also formed in the first year, and the first formation 
of the lamina takes place on the oldest leaves of the young rosette. 
The basifugal apical growth of the lamina of Fern-leaves is however most 
conspicuous when it continually advances for a considerable time without attaining 
a definite conclusion while the lower parts of the lamina have long been fully 
developed, as in Nephrolepis. The periodical interruption of the apical growth 
of the lamina already mentioned occurs in many species of Gleichenia and Alertensia, 
where the development of the leaves remains stationary above the first pair of 
pinnae, and when the pinnation is compound this is often repeated in the several 
orders of branching, so that the apex, forming apparently a bud in the fork, either 
remains altogether undeveloped, or is developed in a succeeding period of vegetation, 
and then only incompletely. This intermittent development of the leaves may 
