512 Wisconsin Academy of Sciences, Arts , and Letters. 
zone (table 7), from the shallow bays (table 10), and from the 
Cladophora belt (tables 11, 12, 13). The total yield, in round 
numbers, is 18,500,000 kilograms wet, 2,100,000 kilograms dry. 
The total area covered by this vegetation is 10,400,000 square me¬ 
ters, or 1,040 hectares. The yield per unit area is therefore 17,788 
kilograms per hectare wet, 2,019 kilograms per hectare dry,—or 
14,867 pounds per acre wet, and 1,801 pounds per acre dry. 
Reference to table 9 makes it evident that, of the total yield, 
nearly one half is found in depths of water of from 1 m. to 3 m. 
More than one quarter is found in water shallower than this, and 
almost exactly one quarter in deeper water. In terms of weight 
per unit area, this means in zone 1 about 16,000 kilograms per 
hectare wet, 1,800 kilograms per hectare dry; in zone 2, about 
24,000 kilograms per hectare wet, 2,700 kilograms per hectare dry; 
in zone 3, about 13,000 kilograms per hectare wet, 1,500 kilograms 
per hectare dry. Converted to pounds per acre, the figures are 
as follows: zone 1, 14,000 wet, 1,600 dry; zone 2, 21,000 wet, 2,400 
dry; zone 3, 11,000 wet, 1,300 dry. 
Comparison of the Quantities of Different Species v Table 8 
shows that, of the above stated total weight, almost half the en¬ 
tire wet weight of plants is made up of Yallisneria. The dry 
weight of this species amounts to about one third of the total 
weight (compare its relatively high water content, table 3). Of 
the remaining species, Potamogeton amplifolius is the most abund¬ 
ant, composing about one quarter of the total. P. Richardsonii 
and P. pectinatus each compose about 10 per cent, of the total 
weight, and all the remaining species are present in much smaller 
quantities, none forming more than 4 per cent, of the total. 
Considering separately the different depth zones, a different situ¬ 
ation is found in each one, except for the common predominance 
of Yallisneria. In the shallow water, the vegetation, exclusive of 
Yallisneria, is composed of about equal quantities of P. pectina¬ 
tus and P. Richardsonii , these two species making up about 30 
per cent, of the total. Najas, Ranunculus, and Chara each com¬ 
pose about 6 per cent. Ceratophyllum and Myriophyllum are 
present only in small quantities. In the middle zone, Potamogeton 
amplifolius replaces to a large extent the other species of Pota¬ 
mogeton, and it is here that Ceratophyllum and Myriophyllum are 
most abundant. Two plants, Potamogeton lucens and Ranuncu¬ 
lus , are not found beyond the shallow zone; and one new species, 
