18 BULLETIN 1191, U. S. DEPARTMENT OF AGRICULTURE. 
down to the thickened margin just above the stipe, but not into the 
stipe. By the time the first cleft is formed grooves for second and 
third have appeared in the now greatly broadened upper portion of 
the dividing leaf. The narrower portion of the leaf shows no indi- 
cation of an additional cleft, but begins to lengthen rapidly to a 
narrow blade. The margin at the lower end of the cleft lengthens 
and thickens rapidly as the new leaf lengthens, so that the broad 
dividing leaf soon has a long stipe. 
At this stage, then, there is a succession of leaves, splitting off 
from the side of a short, broad, thin leaf. These leaves differ but 
little, at first, from basal leaves. Their tips soon tear away from 
the terminal leaf coincident with the rapid lengthening of the stipe 
developed from its margin. The smaller leaves assume a lateral po- 
sition in relation to the broad dividing leaf, but there is nearly always 
a conspicuous offset in the main stipe where a lateral is given off. 
These laterals do not develop long stipes. As they attain the size of 
basal leaves, the first laterals divide in the manner described above, 
and build up clusters of narrow, short-stemmed leaves. The stipe 
of about the third lateral rounds out and becomes a hollow cyst or 
float. The blade borne on this first cyst usually subdivides to form 
a cluster of leaves, which fruit later but do not send up additional 
fronds. Fronds may arise, however, from any leaf cluster below. 
All subsequent laterals develop cysts. From the fifth or sixth, up- 
ward, laterals no longer subdivide, unless accidentally split, but de- 
velop longer and much broader blades than those of leaves at the 
base of the plant. The first cysts formed are more plump and thin- 
ner walled than those usually found on the surface of the water. 
This gives them great buoyancy and enables them to hold the young 
frond in an upright position. As the frond grows, the terminal leaf, 
or, as it might be called, “terminal bud,” gathers momentum in the 
production of laterals, until as many as 20 may be found still at- 
tached to it by their tips. (See Fig. 5.) Just as in other plants, the 
faster the frond grows the more delicate and susceptible to injury the 
“bud” becomes; but unlike the growing bud of a land plant, this 
bud is fully exposed. A measure of protection is afforded, however. 
The rapidly growing terminal leaf outdistances the laterals, espe- 
cially their cysts, so that the leaves on the last two to four feet of a 
vigorous frond have no cysts sufficiently developed to function. Since 
their tissues are slightly heavier than water, such growing tips may 
droop several feet under the surface; thus escaping the destructive 
action of the wind. As the frond approaches the surfacé, the rate of 
growth decreases, the terminal leaf gradually becomes smaller and 
less delicate, and fewer laterals split off, until finally no more are 
formed. 
Usually about six weeks elapse from the time a frond attains the 
surface until leaf formation ceases, but very thrifty fronds may 
grow for a longer period. After division ceases, the laterals con- 
tinue to grow in length and breadth, but most especially in thick- 
ness, and the stipes continue to increase in length and weight; thus 
the frond is gaining weight for about three months. The growing re- 
gion of the leaf gets thicker and tougher with age, so that a mature 
frond is able to withstand all ordinary weathering. The leaves 
borne after attaining the surface of the water are always smaller than 
those a few feet under water and the terminal leaf seldom attains the 
