
observed until late in the fall. A single plant of water-net, when 
viewed closely, is composed of a net as delicate as that of a lady’s 
veil; and each complete mature plant, as can readily be seen in 
young specimens, has the shape of a slender, hollow cylinder, or 
sac, sometimes six or eight inches long, and closed and rounded at 
both ends. Mixed with the Hydrodictyon, there has developed in 
the brook during the past season a small amount of Spirogyra, and 
a few other filamentous algea. The rocks forming the dams at 
the water-falls have been covered largely with a slimy, dark- 
green coating, mainly of Phormidium and other species of blue- 
green algae. 
Under favorable conditions of growth, the Hydrodictyon repro- 
duces very rapidly, by means of a complicated, yet fascinating, 
process called “swarming” of the millions of zoospores, or 
animal-like reproducing cells. 
The rapidity of reproduction of the water-net and the astound- 
ing increase, may be readily explained by the fact that each of the 
7,000 to 20,000 cells which compose the sac-like plant may in turn, 
by the swarming of its contents, produce a new cylindrical net- 
work, composed, like the parent plant, of thousands of cells. 
Thus, every three or four weeks there would result a new crop of 
perhaps 20,000 new plants from each old water-net sac. Starting 
with but a single plant, the increase by geometrical ratio would 
thus, in but a single season, result in unthinkable billions of 
progeny. 
The extraordinary increase of the water-net in the lower pools 
of the brook has given some concern to the Garden authorities, 
who have tried to devise some means of adequate control. Two 
methods of control were suggested: one, the use of copper sul- 
phate, a very dilute solution of which is poisonous to the algae; 
the other, the raking out and final hauling away of the tangled 
scums and algal growths. Up to the present, copper sulphate has 
been applied but once to the brook, and then only to the lowest 
pool. It was realized at the time that this application to the 
lowest pool was practically valueless as an experiment, since the 
stream was constantly carrying down from above bits of algae, 
which would thus serve to replenish the supply almost as fast as 
it could be destroyed by the poison. Another suggestion was to 
en 
