MR. G. SHEPPARD'S letter under this heading, in NATURE of April 25, directs attention to a matter which may be of serious importance. Apparently, the fitid plankton accumulations described were dead material. Years ago, when oil began to be discharged upon the troubled waters of the oceans, some of us suggested that the plankton might suffer. Since then, multitudes of birds have been cast dead upon our shores enwrapped in oil. Occurring as these discoloured patches do, in the steamship lanes, they may be but a fulfilment of our prediction—one which sooner or later must come true: we cannot for ever sin against Nature. Has any attention been paid to such possibility by those who are studying the problem? Forced by modern sanitary practice to send our phosphates to sea, it will be strange if revenge be taken, through the oil wasters who are everywhere fouling the ways of life: through their interference with the recovery of phosphate by plankton.