Section V, 1921 



[23] 



Trans. R.S.C, 



The Effect of Light on Growth in the Mussel 



By A. G. Huntsman, B.A., F.R.S.C. 



(Read May Meeting, 1921) 



At the Atlantic Biological Station a series of experiments was 

 carried through by Miss Mossop in 1919 in an effort to determine 

 the effect of varying natural conditions on the growth of the sea 

 mussel — Mytilns. These conditions were not varied enough to show 

 to what extent light is a determining factor in growth. In the summer 

 of 1920, therefore, I devised and carried through an experiment in 

 which it is believed that light was the only variable factor. 



Two boxes (253^ in. long and 11^:( in. square in cross section) 

 with partly open ends were so constructed that no light could directly 

 penetrate to a central compartment (see Figure 1), and the inner 



Fig. 1 

 Longitudinal section of box used in experiment. 



surfaces were coated with lampblack so as to prevent any light from 

 being reflected to that compartment. As the two partitions in each 

 box were incomplete, water could readily pass lengthwise through it. 



In the top of each box an opening llf in. long gave access to the 

 central compartment, and was closed in one case by a wooden cover 

 and in the other by a glass one. The boxes were fastened beside 

 each other to a floating breakwater, past which a moderately strong 

 tidal current almost constantly flowed. 



After the lapse of nearly a month (Aug. 8 to Sept. 3) it was 

 found that an alga {Ectocarpiis confervoides siliculosus, as kindly 

 identified by Mr. A. B. Klugh) was growing in the central compart- 



