30 BULLETIN 1191, U. S. DEPARTMENT OF AGRICULTURE. 
Of the various explanations offered for the phenomenon, only two 
need be mentioned here. The first is that the heavy mat of kelp, 
composing the atfected beds, shut off the hight from the leaves be- 
low; that this rendered them unable to manufacture the usual amount 
of starch, and evolve sufficient gas to keep the cysts full; that the 
cysts then filled with water, the fronds below sank and dragged 
down the floating mat, which thereupon decayed. There are two 
important objections to this theory: First, the solid tissues of kelp 
are but slightly heavier than water; therefore, even though the 
cysts on the under side of the mat should become completely filled 
with water, the water-logged portions would exert only a slight 
downward pull. So long as the upper layers of the mat remained 
healthy, they would retain their buoyancy, and the bed would not 
sink. Second, kelp decays much less rapidly under water than on 
the surface. Plants that never rise to the surface, except when 
there is no current, are vigorous and free from disease. If a heavy 
kelp bed which has just begun to slough should be submerged for 
a few days by a strong current, it would probably be clean and 
healthy when it rose again to the surface. 
The more plausible explanation is that the kelp died and decayed 
during the hot wave. The United States Wieaihier Bureau reports 
unusually warm weather in the Pacific coast section in July, 1917. 
Capt. W. Engelke reports that a heavy bed of kelp off Canada del 
Capitan completely disappeared in four days’ time during a hot 
wave early in July. At the same time, another bed a few miles to 
the east also disappeared, but a third bed lying between the two 
survived. This middle bed lay opposite the mouth of a canyon 
where, unlike the other two beds, it was exposed to a slight land 
breeze during the hot wave. The water over the area where the 
kelp had disappeared showed the color imparted by decaying kelp. 
The objection may be offered that kelp does not decay so rapidly; 
but in warm weather kelp plants are often thrown up, fresh, in the 
morning, on the beach at La Jolla, and by midafternoon their sporo- 
phyls are rapidly decaying. Young plants carried in an iron 
collecting box, in fairly warm weather, decay to such an extent in 
24 hours that they fall apart when lifted from the box. In explana- 
tion of the kelp’s sinking, instead of sloughing and drifting ashore, 
Mr. Thompson, at Summerland, suggested that the cysts developed 
punctures and then filled with water and sank. Numerous observa- 
tions in the laboratory and in the kelp beds prove that when kelp lies 
exposed to the air for several days, in perfectly cali weather, the 
upper exposed side of the cyst soon decays and develops a puncture. 
In comparatively open kelp beds, when there is plenty of wave motion 
and the cysts have no chance to become dry or sunburned, no punc- 
turing occurs. But the Santa Barbara kelp that sank was all 
densely matted and in three or four days of perfectly still, warm 
weather, enough puncturing could have occurred to sink it. 
These kelp beds were slow to reappear, the one at Canada del 
Capitan not appearing again until the following March. From 
various observations of dead holdfasts, and from data recently 
gathered on the development of young plants, it seems safe to say 
that the old plants in these beds all died, and that the new beds of 
1918 were made up entirely of young plants derived from spcres 
