12 BULLETIN 1191, U. S. DEPARTMENT OF AGRICULTURE. 
thicken and lengthen below, giving rise to the two main arms or 
branches. The outer segments begin to outgrow the inner pair, and 
very soon the serial splits begin to appear, showing their evolution 
into the growing tips of the first two ascending fronds. In some 
plants all the leaves are still attached at their tips to the original 
blade, even after the first cysts have begun to round up. The char- 
acteristic marginal teeth do not appear before the plant has attained 
a height of 5 or 6 inches. <A few teeth then appear below the middle 
of the blade, but none on the thickened margin at the base, from 
which the stipe is derived. A growing tip regularly has a few teeth 
on its outer margin. (Fig. 4.) Teeth appear on the margins of the 
first cleft when it has attained a length of a little more than an inch, 
becoming more conspicuous as the plant approaches maturity, de- 
veloping to their full extent in plants producing stipes and leaves 
of full weight. In large plants they are longer, more widely spaced, 
and turn out more sharply 
from the margins on basal 
sporophyls than on floating 
leaves. None occur on the 
inner margin of a growing 
tip or terminal leaf of a 
frond, since this is being 
continually torn away bit by 
bit as laterals are given off. 
BRANCHING. 
The primary stipe seldom 
attains a length of more 
than 5 inches. The first 
arms attain a length of from 
2 to 4 inches and stand out 
horizontally or curve up- 
#ic. 4.—Middle portion of a plant 5 or 6 months ward. The next interval, 
a old. The first pair of. fronds beginning to rise between the second branch- 
from th, marginal divisions of, tne peimary ing and the first, leaf on the 
center will both split longitudinally. Of the ascending frond, is some- 
velop the second pair of fronds. times. very long, as much. as 
3 feet in some plants. This 
first lateral on the frond is provided with a cyst at its base, indicating 
that the next frond must come from the central pair of leaves, origi- 
nating at the time of the second splitting, since cysted leaves do not 
give rise to fronds, and since fronds or leaves do not originate except 
by the splitting of leaves. When the first two fronds have become 
well started, the central leaves each split symmetrically, and of the 
four leaves thus produced, the central two give rise to fronds. ‘There 
are thus two steps which may be noted in the origin of a frond. The 
first is the splitting of a basal leaf into two nearly equal divisions. 
The second is the transformation of one of these leaves into the 
terminal leaf of a frond. (Fig. 5.) The plant thus always pro- 
vides a leaf from which another frond may arise. Successive fronds 
arise from alternate sides of this basal leaf. We should, therefore, 
expect an old plant to have a short, upright trunk, giving rise to 
two arms zigzagging upward and sending up a frond at each angle. 
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