ADeimberif95m'}        Botany  and  Materia  Medica.  609 
even  in  the  driest  season  of  the  year,  the  contained  moisture  is 
sufficient  to  enable  them  to  put  forth  roots,  a  new  plant  resulting. 
The  function  of  the  spines  in  the  Cactaceae  has  been  generally 
asserted  to  be  largely  for  protection  ;  the  writer  claims  that  the 
cylindrical  opuntias  depend  largely  for  dissemination  upon  the  readi- 
ness with  which  the  branches  break  off  and  upon  the  highly  devel- 
oped barbed  spines.  The  flat  opuntias  are  nearly  all  smooth,  but 
here  the  usual  habit  is  prostrate  or  semi -prostrate,  so  that  the 
branches  bending  or  creeping  take  root  at  the  joints.  The  young 
branches  of  the  plato-puntia  are  likewise  more  easily  detached. 
This  appears  to  be  the  prevailing  method  of  dissemination,  so  much 
so  that  several  species  have  almost  lost  the  power  of  seed  produc- 
tion, and  even  in  species  not  sterile,  owing  to  the  unfavorable 
climate,  the  seed  seldom  germinate. 
This  vice-presidential  address  of  Professor 
Development  of    j  Q  Arthur  5efore  secti0n  G,  of  the  A.  A.  A. 
Vegetable        J  '  ' 
Physiology.       S.,  at  the  Springfield  meeting  in  August,  is 
published  in  the  Botanical  Gazette,  September, 
p.  381,  and  will  repay  careful  perusal.      Physiology  deals  with 
what  plants  do,  their  methods  of  activity,  their  behavior  ;  while  the 
other  divisions  of  botany  treat  of  what  plants  are  or  have  been,  their 
form,  structure  and  relation  of  parts. 
Only  the  vaguest  notions  are  current  regarding  the  nutrition  of 
plants,  the  uses  of  the  leaves,  the  movements  of  sap,  the  purposes 
of  color,  and  the  means  by  which  new  positions  are  assumed.  This 
ignorance  is  primarily  due  to  the  fact  that  almost  nothing  can  be 
learned  of  the  functions  of  plants  from  direct  observation. 
Vegetable  physiology,  as  the  term  is  generally  employed,  is  not 
a  homogeneous  science.  The  most  obvious  distinction  to  be  made 
in  the  physiological  aspect  of  organisms  is  in  regard  to  their  ma- 
turity. In  the  embryonic  or  juvenile  condition,  it  manifests  pecu- 
liarities of  the  highest  import,  quite  unlike  those  of  the  adult.  The 
physiology  of  reproduction  belongs  here,  and  includes  not  only  a 
study  of  the  formation  and  increase  of  the  young  plants,  that  is 
embryology,  but  genesiology  as  well,  that  is,  the  philosophy  of  the 
transmission  of  qualities  and  powers  from  the  parent  to  the  offspring. 
Vines  has  recently  called  attention  to  the  fact  that  even  vegetative 
reproduction,  as  in  the  case  of  the  growth  of  a  plant  from  a  cutting, 
brings  about  rejuvenescence  of  the  protoplasm,  the  new  individual 
showing  the  characters  of  youth  and  not  of  maturity. 
