312 
JOURNAL  OF  HORTICULTURE  AND  COTTAGE  GARDENER 
April  15,  1887. 
Erythrodo*a  of  the  Synopsis  of  the  European  species  prepared  by 
Mr.  J.  G.  Baker.  The  small  white  flowers  are  freely  produced  in 
umbels  on  viscid  scapes  ;  the  rather  small  obovate  leaves  are  dark 
green,  with  closelv  set  teeth,  and  are  ciliated  and  viscid,  or  clammy, 
on  both  sides.  This  Snowy  Primrose  is  said  to  succeed  well  in 
light  soil  in  any  position  on  the  rockery  in  which  it  obtains  plenty 
of  moisture.  In  tbi*  garden  it  does  best  on  a  partially  shaded 
rockery  where  it  receives  a  little  of  the  morning  and  early 
forenoon  sun.  It  is  given  an  adequate  supply  of  water  in  dry 
weather. 
The  Aubrietias  are  great  favourites  of  mine.  They  succeed 
well  here,  and  when  fully  in  bloom  the  effect  they  produce  i«  very 
fine.  They  flower  profusely  and  seed  freely,  with  the  result  that 
self-sown  seedlings  become  very  numerous,  and  these  show  great 
variation  in  shade  of  colouring,  ranging  from  very  pale  lilac  to 
almost  purp’e  or  crimson  purple.  A  named  variety  new  to  me, 
which  was  bought  last  year  under  the  name  of  A.  grandiflora 
Wallacei,  has  been  amoDg  the  earliest  to  cover  itself  with  flower, 
although  some  others  showed  a  few  atray  blooms.  The  flowers  of 
this  variety  are  not  so  large  as  those  of  some  others,  but  are  of  a 
bright  crimson  purple,  which  makes  a  fair  sized  plant  very  effective 
hanging  over  t^e  ledge  of  a  stone  in  the  rock  garden.  We  cannot 
but  admire  these  early  flowers,  which  please  everyone  by  their 
appearance  ere  .winter  has  fairly  gone.  They  are  a  foretaste  of 
milder  days,  when  the  garden  glows  with  colour  and  the  delight  of 
the  lover  of  flowers  is  at  its  zenith. — S.  Arnott. 
CHEMISTRY  IN  THE  GARDEN. 
{Continued  from  page  247.) 
We  have  seen  that  a  mechanical  analysis  of  a  soil  is  a  simple 
but  effective  means  of  determining  the  quantity  of  stones,  sand, 
clay,  and  organic  matter  contained  in  it.  Practical  gardeners  can 
as  a  rule  distinguish  a  good  soil  from  a  bad  one  by  its  appearance, 
but  to  those  not  satisfied  with  empirical  knowledge  the  question 
naturally  arises,  “  What  constitutes  a  good  soil  ?  ”  In  trying  to 
determine  really  what  a  good  soil  is  many  things,  widely  differing 
from  each  other,  must  be  taken  into  consideration,  the  most 
important  being  those  ingredients  which  constitute  the  food  of 
plants. 
What  are  *the  constituents  of  plant  food,  and  how  are  they 
determined  ?  To  answer  these  questions  we  must  ask  the  assist¬ 
ance  of  the  chemist,  who  in  his  laboratory  can  by  analysis  tell  us 
the  names  of  the  substances  which  are  found  in  soils,  and  also  those 
which  are  elaborated  and  built  up  into  the  plant  body.  After 
careful  research  chemists  have  told  ua  that  thirteen  chemical 
substances  are  found  in  all  plants,  and  by  experiments  it  has  been 
found  that,  with  two  exceptions,  all  these  are  essential  to  plants  if 
they  are  to  live  and  develop.  The  names  of  the  thirteen  chemical 
substances  are  as  follows  :  Carbon,  hydrogen,  oxygen,  nitrogen, 
sulphuric  acid,  phosphoric  acid,  potash,  lime,  magnesia,  iron, 
chlorine,  silica,  and  soda.  The  two  exceptions  named  above  are 
silica  and  soda. 
All  the  carbon  and  part  of  the  oxygen  found  in  plants  has  been 
obtained  from  the  carbonic  acid  gas  which  is  in  the  atmosphere, 
the  remaining  oxygen  and  the  greater  part  of  the  hydrogen  beiDg 
derived  from  water.  Given  a  good  supply  of  air  and  water  plants 
under  favourable  conditions  have  an  unlimited  supply  of  carbon, 
hydrogen,  and  oxygen.  Soils  to  be  of  any  value  to  plants  as  food 
must  contain  a  supply  of  potash,  lime,  magnesia,  phosphoric  acid, 
sulphuric  acid,  iron,  chlorine,  and  nitrogen.  Do  they  ?  It  will 
be  a  great  help  to  us  in  answering  this  question  if  we  examine  the 
chemical  analyses  of  a  clayey  soil,  a  loam,  and  a  sandy  soil  ;  for 
then  we  shall  not  only  be  able  to  see  if  they  contain  the  necessary 
constituents  of  plant  food,  but  also  the  amount  of  it  which  each 
contains. 
Analyses  of  Soils. 
Constituents. 
Clayey. 
Loam. 
Sand\r 
Potash  . 
...  0-83 
...  0-36  ... 
Oil 
Soda . 
,,, 
...  0  09 
...  0-05  ... 
0.07 
Lime . 
...  116 
...  0-83  ... 
0-19 
Magnesia  . 
...  0-67 
...  0-47  ... 
013 
Phosphoric  acid 
,,, 
...  0-18 
...  0-12  ... 
009 
Sulphuric  acid 
... 
...  012 
...  0-05  ... 
0  02 
Iron  oxide  ... 
,,, 
...  5-93 
...  4  07  ... 
2  61 
Chlorine  . 
...  0-05 
trace  ... 
trace 
Alumina  . 
5’65 
...  316  ... 
0  86 
Insoluble  silicates  and  sand 
...  78-44 
...  8418  ... 
92-35 
Organic  matter 
...  6-73 
...  5'93 
3-04 
Containing  nitrogen 
... 
...  015 
...  018  ... 
0-13 
100  00 
100  00 
99'60 
The  above  analyses  show  us  at  a  glance  that  all  those  ingre¬ 
dients  which  are  heeded  by  crops  for  their  grdwth  and  development 
are  present  in  all  three  soils.  By  looking  at  the  above  analyses  it 
will  be  seen  that  the  greater  part  of  the  soil  consists  of  insoluble 
silicates  and  sand,  substances  which  are  of  no  value  to  plants  as 
food  ;  but  in  our  consideration  of  a  fertile  soil  we  must  remember 
that  the  mechanical  condition  is  quite  as  essential  for  the  perfect 
divelopment  of  crops  as  the  chemical,  and  although  the  amount  of 
actual  plant  food  appears  small  it  amounts  to  something  considerable 
if  calculated  per  acre.  The  top  9  inches  of  soil  on  an  acre  of  land 
would  weigh  about  3,000,000  lbs.  If  100  lbs.  of  a.clay  soil  contain 
0  83  lbs.  of  potash,  018  of  phosphoric  acid,  and  0T5  of  nitrogen, 
3  000,000  lbs.  would  contain  24,900  lbs.  of  potash,  equal  to 
200  000  lbs.  of  kainit,  5400  lbs.  of  phosphoric  acid,  equal  to 
45  000  lbs.  of  superphosphate  of  lime,  and  4500  of  nitrogen, 
which  is  equal  to  30,000  lbs.  of  nitrate  of  soda. 
We  must  not  suppose,  however,  that  the  vast  amount  of  plant 
food  in  an  acre  of  land,  as  shown  by  an  analysis,  is  in  a  form  suit¬ 
able  to  the  wants  of  plants,  for  only  a  very  small  portion  of  the 
soil  substances  are  of  any  direct  value  to  crops  as  food.  The  »oil 
is  a  substance  of  a  very  complex  nature.  The  plant  food  in  it  is 
present  in  a  variety  of  forms,  some  of  which  are  soluble  in  the  soil 
water,  or  may  be  dissolved  by  the  acid  sap  which  is  exuded  from 
the  tips  of  growing  roots  ;  while  others  are  insoluble  in  the  soil  . 
water,  and  the  acid  sap  cannot  dissolve  them.  The  plant  food 
which  is  present  in  a  form  soluble  in  water,  or  which  may  be  dis¬ 
solved  by  the  roots  of  plants,  is  called  the  active  part  of  the  soil, 
while  the  insoluble  form  is  known  as  the  dormant. 
Agricultural  chemists  do  not  attach  so  much  importance  to  the 
analysis  of  soil  as  they  did  formerly,  but  are  now  investigating  the 
active  part  of  soils,  or  that  portion  which  may  be  dissolved  in 
water  or  weak  acids.  The  analysis  of  the  active  portion  of  soils 
will  no  doubt  prove  of  much  greater  value  to  cultivators  than  a 
complete  analysis  of  a  soil,  for  while  the  latter  method  may  show 
them  how  much  plant  food  a  soil  contains,  the  former  will  tell 
them  whether  it  is  present  in  a  form  suitable  to  the  requirements 
of  our  crops. 
Before  leaving  the  composition  of  soils  it  will  be  advisable, 
•perhaps,  to  give  as  far  as  our  knowledge  goes  a  brief  description  of 
the  form  in  which  plant  food  is  found  in  the  soil. 
Nitrogen  is  present  in  soils  chiefly  as  organic  nitrogen,  which  is 
of  very  little  or  no  direct  value  to  plants.  There  are  also  smaller 
quantities  of  ammonium  salts  and  nitrates  present,  and  it  is  from 
the  last  named  that  plants  obtain  their  chief  supply  of  nitrogen. 
Potash  is  found  in  soils  principally  in  the  form  of  silicate  of 
potash,  and  silicates  of  alumina  and  potash.  It  is  also  found  in 
very  small  quantities  as  nitrate  and  sulphate,  both  soluble  salts, 
and  it  is  chiefly  from  these  two  sources  that  plants  obtain  their 
potash. 
Phosphoric  acid  is  found  in  soils  in  chemical  combination  with 
iron,  alumina,  or  lime.  All  these  forms  are  insoluble  in  water, 
consequently  are  of  no  direct  value  to  plants.  The  acid  sap  of  the 
roots  of  plants,  and  the  carbonic  acid  in  the  soil  water,  will  convert 
the  insoluble  phosphate  of  lime  into  such  a  condition  that  plants 
can  absorb  it. 
Lime  exists  in  soils  principally  as  carbonate  of  lime,  and  also  to 
a  lesser  extent  as  silicate,  nitrate,  phosphate,  and  sulphate.  Plants 
absorb  nearly  the  whole  of  the  lime  they  need  from  one  or  the 
other  of  the  three  last-named  substances.  Magnesia  is  present  in 
soils  principally  in  the  form  of  silicate  and  carbonate  of  magnesia. 
It  is  also  found  in  very  small  quantities  as  sulphate  and  chloride, 
and  these  are  the  source*  from  which  plants  obtain  their  chief 
supply  of  this  substance.  Sulphuric  acid  is  always  found  in  soils 
in  combination  with  iron,  lime,  potash,  or  magnesia  ;  and  plants 
may  absorb  their  sulphur  from  either  of  these  compounds. 
Iron  exists  principally  in  the  form*  of  iron  oxides  or  hydrates  ; 
there  are,  however,  nearly  always  small  quantities  of  sulphate  and 
carbonate  present,  and  plants  may  obtain  their  iron  from  either  of 
the  two  latter-named  sources.  Soda  is  found  in  soils  either  as 
silicate  or  chloride  of  soda  (common  salt).  Chlorine  is  present  in 
most  soils,  only  in  very  small  quantities.  It  is  generally  found  in 
chemical  combination  with  soda,  forming  chloride  of  soda,  and  it  ia 
from  this  lource  that  plants  obtain  their  chief  supply  of  *oda  and 
chlorine. — W.  Dyke. 
(To  be  continued  ) 
Highgate  Wood. — We  learn  that  tbe  Committee  appointed  to 
secure  the  Churchyard  Bottom  Wotd  at  Highgate  for  the  use  of  the 
public  has  been  taking  active  measures  for  that  purpose.  About  £15,000 
remains  to  be  raised  to  cover  the  purchase  of  the  ground,  and  circulars 
have  been  issued  to  tbe  public  giving  particulars  of  the  project  and 
appealing  for  aid.  Highgate  Wood,  in  tbe  opinion  of  the  Chairman  of 
the  Committee,  i«  *'on«  of  the  choicest  and  mcst  sylvan  pieces  of  wood¬ 
land  which  is  to  be  found  anywleie  withiD  tbe  five  mile  radius  of 
Charing  Cross.”  Mr.  L'o-nel  Cut  tie,  1  Great  College  Street,  Westminster, 
is  the  Secretary  of  the  Fund. 
