﻿288 
  PROCEEDINGS 
  OP 
  THE 
  CALIFORNIA 
  

  

  of 
  Mount 
  Tamalpais. 
  Third 
  ; 
  the 
  oak-groves 
  of 
  San 
  Jos^ 
  Valley, 
  covering 
  

   about 
  250 
  square 
  miles. 
  Fourth 
  ; 
  mixed 
  groves 
  of 
  oaks 
  and 
  pines 
  on 
  the 
  east- 
  

   erly 
  slopes 
  of 
  the 
  Contra 
  Costa 
  and 
  Mount 
  Hamilton 
  Ranges. 
  Fifth 
  ; 
  similar 
  

   groves 
  on 
  the 
  ranges 
  north 
  of 
  the 
  Bay, 
  forming 
  the 
  continuation 
  of 
  those 
  

   mountains. 
  

  

  The 
  modifications 
  caused 
  in 
  the 
  course 
  and 
  force 
  of 
  the 
  wind 
  by 
  the 
  various 
  

   gaps 
  referred 
  to, 
  are 
  the 
  chief 
  causes 
  of 
  local 
  peculiarities 
  in 
  the 
  distribution 
  of 
  

   trees. 
  The 
  shelter 
  afforded 
  by 
  the 
  intervening 
  mountain 
  ranges, 
  and 
  by 
  others, 
  

   farther 
  inland, 
  together 
  with 
  the 
  directions 
  and 
  width 
  of 
  the 
  valleys, 
  so 
  modify 
  

   the 
  distribution 
  of 
  species, 
  that 
  instead 
  of 
  being 
  in 
  semi-circles 
  concentric 
  to 
  

   the 
  " 
  Golden 
  Gate," 
  they 
  are 
  found 
  to 
  be 
  arranged 
  in 
  semi-ellipses, 
  with 
  curves 
  

   nearly 
  parallel 
  to 
  that 
  of 
  an 
  arc 
  drawn 
  from 
  Point 
  Reyes, 
  through 
  the 
  Golden 
  

   Gate, 
  to 
  Pigeon 
  Point. 
  

  

  Of 
  course, 
  the 
  general 
  law 
  of 
  increase 
  in 
  number 
  of 
  species 
  and 
  individuals 
  

   toward 
  the 
  north, 
  in 
  direct 
  proportion 
  to 
  the 
  increase 
  of 
  moisture, 
  and 
  their 
  de- 
  

   crease 
  toward 
  the 
  south 
  and 
  east 
  ( 
  at 
  the 
  sea-level 
  ) 
  from 
  the 
  contrary 
  condi- 
  

   tions, 
  has 
  its 
  full 
  eSect 
  in 
  this 
  region. 
  

  

  We 
  thus 
  have 
  three 
  primary 
  groups 
  of 
  trees 
  — 
  the 
  Northern, 
  Southern, 
  and 
  

   Eastern 
  ; 
  but 
  within 
  the 
  limits 
  mentioned, 
  only 
  two 
  are 
  exclusively 
  northern, 
  if, 
  

   indeed, 
  more 
  than 
  varieties 
  of 
  southern 
  forms 
  {Cup, 
  Mamahiana 
  and 
  Pinus 
  

   contm-ta). 
  Those 
  confined 
  to 
  the 
  south 
  are 
  but 
  three, 
  of 
  which 
  two, 
  the 
  Grape 
  

   and 
  Sycamore, 
  go 
  north 
  in 
  the 
  Sacramento 
  Valley 
  ; 
  while 
  the 
  Pine 
  ( 
  P. 
  in- 
  

   signis 
  ) 
  has 
  been 
  confounded 
  with 
  northern 
  forms, 
  and 
  may 
  be 
  only 
  a 
  local 
  

   variety. 
  

  

  The 
  Eastern 
  Group 
  contains 
  four 
  species, 
  Juglans 
  rupestris, 
  Juniperus, 
  (sp.) 
  

   Pinus 
  Sabmiana, 
  and 
  P. 
  Coulteri, 
  of 
  which 
  the 
  second 
  is 
  a 
  rare 
  straggler 
  ; 
  and 
  

   the 
  fourtb 
  closely 
  allied 
  to 
  the 
  third. 
  To 
  counterbalance 
  this, 
  is 
  a 
  group 
  con- 
  

   fined 
  to 
  the 
  Coast, 
  not 
  found 
  east 
  of 
  the 
  Bay, 
  consisting 
  of 
  four 
  or 
  five 
  species 
  : 
  

   Fraxiims 
  Oregonus, 
  Quercus 
  chrijsolepis, 
  Torrcya 
  Calif 
  ornica, 
  and 
  Taxus 
  

   hrevifolia; 
  probably, 
  also, 
  Cupressus 
  macrocarpa. 
  

  

  The 
  remaining 
  twenty-seven 
  are 
  found 
  around 
  three 
  sides 
  of 
  the 
  Bay, 
  and, 
  

   therefore, 
  show 
  most 
  strongly 
  the 
  influence 
  of 
  the 
  sea-breeze 
  in 
  limiting 
  their 
  

   approach 
  to 
  its 
  mouth. 
  Fourteen 
  of 
  these 
  may 
  be 
  considered 
  as 
  scarcely 
  limited 
  

   by 
  it 
  at 
  all, 
  since 
  they 
  are 
  found 
  within 
  the 
  most 
  windy 
  portion 
  wherever 
  

   hills 
  furnish 
  a 
  little 
  shelter. 
  From 
  their 
  adaptation 
  to 
  the 
  extremes 
  of 
  our 
  

   climate, 
  they 
  are 
  characteristic 
  of 
  nearly 
  all 
  the 
  mountain 
  ranges 
  of 
  the 
  Bay 
  

   Region. 
  The 
  Fir 
  alone 
  is 
  very 
  rare 
  east 
  of 
  the 
  Bay 
  ; 
  while 
  the 
  Willows 
  and 
  

   Poplars 
  belong 
  to 
  low, 
  wet 
  grounds. 
  Six, 
  being 
  broad-leaved 
  evergreens, 
  and 
  

   one 
  coniferous, 
  show 
  the 
  characteristic 
  proportion 
  of 
  those 
  groups 
  in 
  a 
  region 
  

   almost 
  without 
  frost, 
  but 
  with 
  very 
  moderate 
  summer 
  heat. 
  It 
  is, 
  however, 
  to 
  

   be 
  observed, 
  that 
  nearly 
  all 
  of 
  them 
  flourish 
  more 
  luxuriantly 
  where 
  the 
  summer 
  

   is 
  warmer, 
  even 
  if 
  the 
  winter 
  be 
  colder. 
  

  

  They 
  are 
  the 
  following 
  : 
  

  

  Group 
  I. 
  — 
  Growing 
  within 
  ten 
  miles 
  of 
  the 
  center 
  of 
  San 
  Francisco 
  county 
  : 
  

  

  1. 
  Ceanothus 
  thyrsiflorus, 
  Esch. 
  Wild 
  Lilac. 
  

  

  