320 SECTIONAL TRANSACTIONS.—D. 
and carbohydrate production. ‘The anomaly apparently exists that a water 
may have adequate supplies of nutritive salts and yet a comparatively small 
algal flora. 
Mr. J. T. SauNDERS.— Temperature observations and water movements 
in lakes. 
Mr. F. T. K. PENrELow.—The food of some freshwater fishes. 
Dr. B. Barnes.—The biology of aquatic fungt. 
Freshwater fungi belong chiefly to the Archimycetes and Oomycetes ; 
species of Zygomycetes and of Ascomycetes are few, and Basidiomycetes 
seem to be unrepresented. 
Our knowledge of the biology of aquatic fungi is scanty, based on inci- 
dental observations. No one seems to have studied the fungal population 
of a piece of water over a period of years. 
The Archimycetes are mostly parasites, attacking other fungi, alge and 
animals. Some are saprophytes, and it is possible that the virulence of 
the parasitic species has been over-stressed. ‘The Oomycetes are mostly 
saprophytes, some having a remarkable tolerance of bacterial associates. 
Oomycetes appear to be most abundant in the colder parts of the year, 
but since vegetable debris gathered in summer has yielded good fungal 
growth after a few days at low temperatures, it seems likely that some 
mycelium persists throughout the year. 
So far as can be judged, fungi are not normally prominent members of 
the aquatic population. As, however, they grow and multiply rapidly, special 
conditions may induce mass occurrence, such as is well known in Lepto- 
mitus in contaminated water. 
AFTERNOON. 
Discussion on The inheritance of productivity (2.15) :— 
Mr. Joun HammMonp.—Meat. 
Introduction —Almost all the characters of any importance for meat are 
dependent for their full expression on nutrition. The mutations which 
occur are nearly all recessive and consist of defects or fancy points. Com- 
mercial qualities are formed by the accumulation of small variations 
developed in response to the environment, and exist in varying degrees of 
fixity. Evolution of the gene has to be considered as well as mutation of 
the gene. These principles are illustrated by the evolution of the horse 
and by reciprocal Shire-Shetland crosses. 
Cattle (beef and veal).—Selection for beef conformation is only effective 
under nutritional conditions which develop the characters. The directive 
influence of man’s selection is shown by a comparison of age changes in the 
conformation of breeds of different origin bred for the same purpose. Large 
mutations (Doppellender calves for veal) play no part in the evolution of 
beef cattle. Body fat colour requires a definite environment of food supply 
before selection can be made for the genetic factors concerned. 
Sheep (mutton and lamb).—The proportions of bone, muscle and fat in 
different breeds and crosses are developmental characters which depend 
on nutrition. Crosses between these ‘ developed ’ types of different levels 
give intermediates which do not segregate sharply as do those of a mutation 
(Ancon sheep). 
Pigs (bacon, pork and lard).—Local feed conditions have supplied the 
