﻿198 
  REPOET 
  OF 
  COMMISSIONER 
  OF 
  l^ISH 
  AND 
  FISHERIES. 
  

  

  the 
  surface. 
  As 
  the 
  conditions 
  of 
  the 
  bottom 
  change 
  from 
  year 
  to 
  

   year 
  the 
  growth 
  gradually 
  spreads 
  from 
  one 
  place 
  to 
  another. 
  In 
  

   this 
  mass 
  of 
  vegetation 
  clams 
  are 
  often 
  found 
  in 
  numbers, 
  even 
  when 
  

   the 
  soil 
  is 
  almost 
  pure 
  sand 
  and 
  the 
  currents 
  are 
  swift. 
  The 
  reason 
  

   that 
  they 
  are 
  able 
  to 
  establish 
  themselves 
  is 
  that 
  the 
  growth 
  of 
  so 
  many 
  

   plants 
  prevents 
  any 
  shifting 
  of 
  the 
  bottom, 
  and 
  still 
  does 
  not 
  interfere 
  

   greatly 
  with 
  the 
  food 
  supply. 
  

  

  On 
  account 
  of 
  the 
  long 
  wire-like 
  roots 
  it 
  is 
  very 
  difficult 
  to 
  dig 
  these 
  

   tracts, 
  and 
  in 
  view 
  of 
  the 
  sadly 
  depleted 
  condition 
  of 
  our 
  beaches 
  and 
  

   flats 
  the 
  circumstance 
  is 
  a 
  fortunate 
  one, 
  for 
  there 
  is 
  preserved 
  in 
  

   these 
  beds 
  a 
  supply 
  of 
  breeding 
  individuals 
  which, 
  if 
  proper 
  methods 
  

   are 
  employed, 
  may 
  reestablish 
  areas 
  rendered 
  barren 
  by 
  excessive 
  dig- 
  

   ding. 
  

  

  Figure 
  1 
  shows 
  a 
  clam 
  bed 
  artificially 
  constructed 
  in 
  an 
  immense 
  

   field 
  of 
  thatch 
  by 
  removing 
  the 
  vegetation. 
  Many 
  of 
  the 
  roots 
  of 
  the 
  

   plants 
  still 
  remain, 
  however, 
  and 
  hold 
  the 
  soil 
  firmly. 
  Figure 
  2 
  rep- 
  

   resents 
  a 
  few 
  feet 
  of 
  the 
  surface 
  of 
  this 
  bed, 
  the 
  numerous 
  siphon 
  

   holes 
  indicating 
  the 
  great 
  number 
  of 
  young 
  supplied 
  by 
  parent 
  clams 
  

   living 
  in 
  the 
  undisturbed 
  thatch. 
  

  

  In 
  the 
  eelgrass, 
  which 
  grows 
  between 
  the 
  tide 
  lines 
  as 
  well 
  as 
  below, 
  

   clams 
  may 
  also 
  sometimes 
  be 
  found, 
  but 
  they 
  are 
  not 
  numerous. 
  Like 
  

   the 
  thatch, 
  the 
  eelgrass 
  prevents 
  the 
  erosion 
  of 
  the 
  bottom, 
  but 
  also 
  

   probably 
  makes 
  it 
  impossible 
  for 
  the 
  clams 
  to 
  obtain 
  a 
  large 
  amount 
  

   of 
  food, 
  and, 
  moreover, 
  such 
  areas 
  contain 
  a 
  large 
  amount 
  ol 
  decaying 
  

   vegetable 
  matter. 
  

  

  FOOD 
  AND 
  WATER 
  CURRENTS 
  AS 
  CONDITIONS 
  OF 
  CLAM 
  GROWTH. 
  

  

  The 
  food 
  of 
  clams 
  is 
  chiefly 
  diatoms. 
  Many 
  species 
  of 
  these 
  micro- 
  

   scopic 
  plants 
  are 
  attached 
  to 
  solid 
  bodies, 
  but 
  those 
  used 
  by 
  the 
  clam 
  

   for 
  food 
  swim 
  and 
  float 
  in 
  the 
  water. 
  Their 
  number 
  is 
  enormously 
  

   great, 
  and 
  their 
  distribution 
  apparently 
  as 
  wide 
  as 
  the 
  seas, 
  for 
  they 
  

   occur 
  not 
  only 
  in 
  all 
  the 
  shallow 
  coast 
  waters, 
  but 
  in 
  the 
  depths 
  of 
  the 
  

   ocean 
  as 
  well. 
  They 
  form 
  the 
  food 
  of 
  many 
  marine 
  animals, 
  but 
  prob- 
  

   ably 
  no 
  forms 
  are 
  more 
  completely 
  dependent 
  upon 
  them 
  than 
  the 
  

   group 
  of 
  mollusks 
  to 
  which 
  the 
  clam 
  belongs. 
  If 
  one 
  should 
  follow 
  

   a 
  (^oast 
  line, 
  examining 
  the 
  water 
  in 
  every 
  small 
  bay 
  and 
  off 
  every 
  

   point, 
  in 
  every 
  pool 
  and 
  eddy, 
  and 
  ever}^ 
  swift 
  stream, 
  he 
  would 
  prob- 
  

   ably 
  find 
  diatoms 
  constantly 
  more 
  numerous 
  in 
  some 
  localities 
  than 
  in 
  

   others. 
  The 
  reasons 
  for 
  this 
  may 
  be 
  that 
  salts 
  in 
  solution, 
  which 
  the 
  

   diatoms 
  use 
  for 
  food, 
  are 
  in 
  greater 
  quantity 
  in 
  one 
  place 
  than 
  in 
  

   another, 
  and 
  the 
  differences 
  in 
  temperature 
  affect 
  the 
  rate 
  of 
  reproduc- 
  

   tion, 
  though 
  this 
  is 
  usually 
  a 
  matter 
  of 
  some 
  days. 
  But 
  whether 
  or 
  

   not 
  clam 
  food 
  in 
  a 
  given 
  volume 
  of 
  water 
  is 
  more 
  abundant 
  in 
  one 
  

   place 
  than 
  in 
  another, 
  some 
  of 
  it 
  is 
  present 
  everywhere, 
  so 
  this 
  condi- 
  

   tion 
  of 
  clam 
  growth 
  may 
  be 
  regarded 
  as 
  a 
  constant 
  one. 
  

  

  