VENUS MERCENARIA I9 



14.5 c.cm, or 3.22 times as great. The increase in volume *n the 

 six months, therefore, was 222^. 



Growth between tide lines 



The most important point brought out in this experiment is the 

 fact that growth is considerable on bottoms exposed for several 

 hours at low tide. This is shown in the following cases. 



A line of flowerpots was run from below ordinary low water 

 mark up the steeply sloping beach to a point about two feet below 

 the ordinary high water line, the fall of the tide being about six 

 feet. The pots were sunk so that their tops were level with the 

 ground, and were separated by a space of about two feet. June 19, 

 1901, there was placed in each of these pots a clam 1.25 inches, or — 

 to give the measurements for convenience's sake in sixteenths of 

 one inch — ly^ inches in length. These were examined, after an 

 interval of six months, on Dec. 28. Some of the pots were empty 

 or contained dead shells. In the first or highest, the clam had 

 grown to a length of \\\ inches, an increase of 148^ in volume in 

 the half year. If we had no other example of growth, this would 

 be very suggestive, for the increase is great, the creature having 

 become in this short period almost two and a half times as large 

 as when planted. 



We should expect to find still greater growth with longer 

 immersion. In the second pot, the clam had increased 154^, and 

 in the third, still lower down, 172^. 



The fourth pot was empty. In the fifth, the increase, instead of 

 being greater still, was only 87^. The explanation of this seems to 

 be perfectly clear, and is exemplified in several other cases. Around 

 the margin of this pot there had grown a large quantity of Ulva. 

 There was much of it at this level of the beach, while higher up 

 it was not abundant. Without doubt this seaweed was flattened 

 out over the top of the pot by the current, in such a way as to 

 prevent free access to the food-bearing stream, and for this reason 

 growth was not so rapid. 



The presence of these weeds, which grow on so many bottoms, 

 should not seriously inconvenience the clam culturist. They may 

 be removed without difficulty with a rake, and do not grow 

 abundantly on a surface which is reasonably smooth. If it had 



