Supplement  In 
March  12,  1903.  JOURNAL  OF  HORTICULTURE  AND  COTTAGE  GARDENER.  231 
must  be  taken  into  consideration  that  in  most  cases  the  chances 
are  that  only  one  or  a  few  seeds  at  a  time  of  any  given  plant  would 
be  likely  to  be  carried  to  a  distant  suitable  habitat  where  it  did 
not  already  grow,  and  the  more  distant  the  habitat  the  fewer 
are  the  chances  of  a  plant  reaching  it. 
As  to  the  third  q^uestion,  we  find  that  the  distribution  of  the  | 
Primrose  extends  latitudinally  from  Southern  Norway  and  Sweden  | 
to  Algeria  in  North  Africa  and  Crete,  and  longitudinally  from  the  , 
British  Isles  and  Western  Europe,  through  central  and  southern 
Europe  to  the  Caspian  Sea  and  North-East  Persia.  As  the  plant 
has  such  a  wide  range,  why  does  it  not  extend  further  to  the 
north,  south,  or  east?  There  are  doubtless  many  places  not  far 
outside  its  range  where  it  might  be  expected  to  occur,  and  yet 
from  which  it  is  absent.  It  may  be,  of  course,  that  it  has  not 
succeeded  in  getting  there,  but  as  the  same  iDhenomenon  of  limi¬ 
tation,  but  differing  in  extent,  applies  to  a  vast  number  of  other 
plants,  it  is  clear  that  there  is  some  potent  cause  which  operates 
on  all  alike.  Observation  and  experiment  have  demonstrated  that 
the  two  factors,  heat  and  moisture,  are  the  dominant  arbiters 
which  determine  the  total  range  of  a  plant.  Now  there  is  a 
definite  combined  annual  amount  of  heat  and  moisture  absolutely 
nocesiary  to  the  life  of  every  plant,  varying  in  degree  with 
different  species,  and  when  the  seasonal  amount  of  heat  or  the 
amount  of  moisture  proportional  to  it  falls  short  of  the  necessary 
minimum,  or  is  in  excess  of  the  absolute  maximum  for  a  prolonged 
period,  then  the  plant  cannot  live  under  those  conditions,  and 
climate  thus  presents  a 
natural  barrier  to  its 
further  extension.  It  is 
chiefly  due  to  the  studies  of 
French  philosophers,  espe¬ 
cially  of  Boussingault, 
Adamson,  and  Alphonse 
De  Candolle,  that  we  owe 
a  clear  perception  of  the 
influence  of  heat  upon 
plants. 
The  former  has  taught 
us  that  if  we  multiply 
the  number  of  days 
dui’ing  whieh  a  plant  is 
actively  vegetating  —  that 
is,  in  the  case  of  a  peren¬ 
nial,  from  the  first  signs 
cf  leafing  to  the  fall  of  the 
leaves,  or  in  an  annual 
from  germination  to  the 
ripeningof  the  seeds — by  the 
average  temperature  of  the 
entire  period,  the  product 
will  be  nearly  the  same  for 
that  plant  in  each  year  and 
in  all  countries.  Whilst 
to  Adamson  we  are  indebted 
for  the  following  rule, 
viz.,  if  we  add  together  the 
average  daily  temperatures 
from  the  beginning  of  each 
year,  we  shall  find  that  when 
the  amount  of  heat  approxi¬ 
mately  reaches  certain 
totals,  the  same  oceurrehce 
in  vegetative  activity  (of 
leafing,  flowering,  and 
fruiting)  will  take  place  in 
every  year.  These  state¬ 
ments  point  out  that  for  a  i.  •  a 
plant  to  perfect  its  flowerand  ripen  seeds, it rieeds  a  certam  clehnitc 
amount  of  heat,  which  would  vary  for  each  species,  and  it  that 
necessary  amount  is  not  forthcoming  the  plant  cannot  reproduce 
itself  hence  its  polar  extension  would  be  limited  from  that  cause, 
as  well  as  by  a  low  winter  temperature,  which  its  constitution 
is  incapable  of  withstanding.  Many  plants  are  able  to  with¬ 
stand  a  few  degrees  of  frost  uninjured,  but  when  submitted  to 
20deg  to  30  de-o-  Falir.,  especially  for  several  successive  days,  are 
killed,  so  that  although  the  summer  climate  of  a  country  may  be 
quite  suitable  for  a  plant’s  needs,  yet  the  absolute  temperature 
of  winter,  if  too  cold  for  it,  effectually  prevents  it,  if  a  perennial, 
from  establishing  itself.  This  is  probably  the  reason  why  the 
Primrose  does  not  extend  up  to  the  same  latitude  in  Russia  as 
it  does  in  the  British  Isles,  the  absolute  temperature  of  winter 
being  too  low  for  it.  ,  ^  i  -  j.i  • 
Annuals,  however,  have  solved  the  problem  of  how  to  thme 
in  countries  where,  if  penennials,  they  would  soon  perish.  lor 
although  their  vegetative  organs  are  injurecl  by  frost,  experiinent 
has  demonstrated  that  seeds  will  retain  their  vitality  umnipaired 
even  when  submitted  to  more  than  200deg  of  frost,  if  they 
are  kept  dry  and  not  thawed  suddenly.  By  nature 
annuals  fear'  cold,  and  quickly  respond  to  heat,  grow 
rapidly,  and  quickly  ripen  their  seeds.  Even  tropical  annuals,  in 
the  hot  summers  experienced  in  tcmpeiate  latitudes  in  the  in¬ 
Primula,  Veitcli’s  Double  White  (Page  235.) 
terior  of  continents,  will  thrive  and  ripen  their  seeds;  for  ex¬ 
ample,  the  Maize  will  ripen  at  about  50deg  north  latitude  in  the 
centre  of  North  America,  whilst  in  the  British  Isles,  in  the  same 
latitude,  it  fails  to  do  so,  the  heat  of  our  summer  being  less  than 
the  minimum  amount  reciiiired. 
Having  thus  seen  how  temperature  limits  the  polar  extension 
of  a  plant,  it  may  not  bo  out  of  place  to  briefly  point  out  how 
this  important  factor  affects  plant  life.  Let  us  suppose  that  a 
plant  at  its  extreme  polar  limit  passes  through  all  its  stages  from 
the  first  .signs  of  leafing  to  the  complete  ripening  of  its  seeds  in 
six  months,  or  180  days,  and  computed  by  daily  averages,  accord¬ 
ing  to  Boiissingault’s  method,  receives  during  that  period  a  total 
amount  of  10,000  deg  Fahr.  of  heat,  we  may  accept  it  as  a  fact 
that  that  is  about  the  smallest  amount  of  heat  with  which  it  can 
pei’fect  its  seeds. 
In  following  this  out  it  will  be  noted  that  during  the  180  days 
the  daily  average  temperature  will  be  very  much  higher  during 
the  period  between  the  flowering  and  maturity  of  the  seeds  than 
at  any  other  period,  and  it  can  be  proved  by  experiment  that  this 
is  absolutely  necessary,  for  if  the  temperature  at  that  period 
docs  not  rise  sufficiently  high,  fully  ripened  seeds  will  not  be 
obtained.  As  an  example  of  this  the  occasional  failure  of  the 
M^lieat  crops  in  the  Britisli  Isles  may  be  cited.  The  average  daily 
temperature  for  the  two  hottest  months  (July  and  August)  is 
about  Oldeg  or  62deg  Fahr.,  and  when  we  get  a  cool  summer,  and 
the  temperature  of  these  months  falls  to  an  average  of  57deg  or 
58deg,  the  \Vhca.t  does  not 
mature.  Also,  if  the  total 
amount  of  heat  needed  is 
spread  over  the  longer 
period  of  time,  this  would 
lower  the  average  tem¬ 
perature  and  prevent  the 
seeds  from  properly  matur¬ 
ing. 
On  the  other  hand,  if  the 
entire  period  only  occupied 
120  or  130  instead  of  180 
days,  then  the  average  daily 
temperature  would  be  much 
greater,  and  would  greatly 
affect  the  quality  of  the  fruit 
and  seed.  This  is  a  very 
important  point  to  the  gar¬ 
dener  and  agriculturist. 
Although  sunlight  cannot 
be  controlled,  artificial  heat 
can,  and  by  a  proper  know¬ 
ledge  of  the  amount  re¬ 
quired,  and  a’judieious  ap¬ 
plication  of  it,  many  plants 
may  be  made  to  flower  or 
ripen  fruit  at  any  particular 
time  required,  the  quality 
of  the  fruit  being  secured 
by  the  proper  adjustnunc  of 
high  temperatures  at  the 
right  time.  For  it  is  found 
that  a  high  day  temperature 
and  lower  night  temperature 
(providing  it  is  not  too  low), 
produce  a  much  better 
quality  of  fruit  than  if  the 
same  total  amount  were 
supplied  by  an  even  tem¬ 
perature  throughout — that 
is  to  say,  alternate  tempera¬ 
tures  of  flfideg  and  fiOdeg  Fahr.,  would  give  better  results  than 
an  uniform  one  of  78deg. — N.  E.  Beown. 
(To  be  continued.) 
Flowers  v.  Tea. 
It  is  not  perhaps  generally  known  that  the  flower  petals  of 
Roses,  Olea  fragrans.  Tuberose,  Orange,  Jes.samine,  Gardenia,  and 
Azalea  ai’e  largely  used  to  perfuma  the  teas  we  drink,  though  the 
name  Orange  Pekoo  might,  perhaps,  have  suggested  this  fact. 
The  Chinese  call  this  tea  by  a  name  meaning  superior  perfume, 
while  the  pure  Pekoe  i.s  called  Lau-tsze’s  eyebrows.  It  should 
be  explained  that  Pekoe  means  “  white  hair,”  and  is  applied  to 
the  young  tea  leaves  owing  to  the  fact  that  they  are  covered 
with  a  fine  white  down.  Most  of  this  tea  is  sent  to  this  eountry 
or  Russia,  Avliere  it  constitutes  the  bulk  of  the  famous  caravan 
tea  sent  overland.  Lau-tsze  was  the  founder  of  the  Taoist 
religion,  but  as  he  was  born  about  a  thousand  years  before  the 
earliest  mention  of  tea.  we  may  i)resume  ho  never  realised  the 
virtue  of  his  own  eyebrows  as  a  beverage.  Otlnq-  interesting 
Chinese  names  are  “Carnation  Hair,”  “  Red-Plum-blossom .” 
“  Lotous  Kernel,”  “Sparrow’s  Tongue,” 
Dragon’s  Whiskers 
Autumn  Dew,”  and 
“  Dragon’s  Pellet,” 
‘  Pearl  Flower.” 
