ae 
extensively in the relict pools of the emerging bottom-lands, a seed- 
bed for re-stocking the waters of overflow is formed with each declin- 
ing flood, and this seed-bed becomes potent only when floods return. 
The absence of an autumnal overflow and the minor part that the 
autumnal overturning plays in our shallow waters when 39.2° is 
passed, may alike tend to suppress here the autumnal or midwinter 
pulses which occur elsewhere in deeper water. 
The occurrence of the vernal pulse of Asterzonella in the last days 
of April brings it into close relation with the major volumetric pulse 
of the year (Pt. I., Pl. [X.—XII.). - It isnot only an important con- 
stituent of this spring maximum, but it is one of the most prominent 
primal sources of food of the Entomostraca—Bosmina, Daphnia, 
Cyclops, and Diaptomus, all of which exhibit an increase in numbers 
at this period. It shares with Cyclotella the claim to the first place 
quantitatively among the synthetic organisms upon which the 
early spring plankton depends for its development. 
Our records are all based upon the catches of the silk net, through 
whose meshes the isolated cells of Asterionella readily escape. Filter- 
paper catches give much higher numbers except during the period of 
maximum, when the numbers by the two methods do not materially 
differ. This seems to be due to the fact that isolated cells are rela- 
tively much more abundant after the maxima than they are be- 
fore them, and especially at the time of their appearance. These 
diatoms form arcs, circles, or whorls, of a varying number of cells. 
During the vernal pulses of 1898 the average number in these clus- 
ters in the middle of March was three or four, and at the time of the 
maximum on April 26 it rose to five or six, often reaching sixteen or 
more. A fortnight after this maximum the average fell to 1.4, rising 
again with the second pulse, on June 14, to 8.4, and declining in three 
weeks, with the fading out of the pulse, to 1.2. 
Astertonella is frequently infested with great numbers of a minute 
craspemonad flagellate protozoan which appears in thick-set rows 
upon the ray-like cells, a single cell sometimes bearing a score of 
these organisms. This diatom exhibits considerable variation in size 
and proportions. The longer and more slender cells appear at the 
times of the maxima. 
Cocconets communis Heib.*—Average number, 520,000, but more 
than three times as abundant in 1897. This diatom occurs some- 
what irregularly in the filter-paper collections, and has been recorded 
