978 Proceedings of Royal Society of Edinburgh. [sess. 
and natans are aquatic forms of S. simplex, Huds. Plastic 
forms of simplex are seen in var. longissimus, Fries., from 
which a course to minimum is quite open. The terrestrial 
forms of minimum mentioned above seem indicative of a 
reversion towards a terrestrial ancestor. 
POTAMOGETONACEiE. 
Potamogeton natans, L. I., II., III., Abundant everywhere. 
Potamogeton natans, L. I. Dwarf terrestrial forms about 
the shores of lochs ; not common. 
Potamogeton natans, L., app. polygonifolius, Pourr. I. A 
curious dwarf plant about 4 in. long, with the leaves of 
polygonifolius. From a cold spring at the margin of a 
small loch in Ealmacaan Forest, elevation 1600 ft. The 
temperature of the water of this spring was 51*8° F. At 
12 ft. distant the temperature of the water was 57*2° F. At 
the other side of the loch the temperature of the water was 
64'2° F. Air temperature, 54'8° F. There were numbers 
of the normal P. natans about the loch ; but none of this 
depauperated form beyond the cold spring. This plant has 
probably been depauperated from normal forms by its 
habitat ; the specimens were fruiting. 
Potamogeton natans, L ., app. polygonifolius, Pourr. I. Large 
forms universal in peaty lochs. 
Potamogeton polygonifolius, Pourr. I. In less peaty water • 
not abundant. P. natans and polygonifolius, with the 
various intermediate forms, are probably deviations from 
or towards the typical natans. The recent remarks on 
other variable plants may be applied to these. 
Potamogeton heterophyllus, Schreb. III. Extremely abundant 
in L. Cran. 
Potamogeton lucens, L. I., II. Abundant, and universally 
distributed. I have seen very large specimens of this plant 
in Lochan a Chait, below Ben Lawers. 
Potamogeton prselongus, Wulf. I. In less peaty lochs 
distribution very restricted. 
Potamogeton crispus, L. I. Distribution restricted. 
Potamogeton perfoliatus, L. I. Only observed an attenuated 
