28  Contamination  of  Drinking  Water.     {A j^wyfww.1"' 
Structurally,  the  Schizophyceae  are  very  simple  indeed.  Many  of 
them  consist  of  but  a  single  cell,  and  multiply  by  merely  dividing 
and  giving  rise  to  two  cells  like  the  parent.  Others  are  composed  of 
a  series  or  chain  of  cells  which  are  held  together  by  a  gelatinous  en- 
velope, or  there  may  be  direct  protoplasmic  communication  between 
the  cells.  The  contents,  however,  vary  but  little  with  the  external 
appearance  of  the  forms.  While  the  cells  are  filled  with  protoplasm 
and  have  the  usual  granules,  vacuoles,  etc.,  it  is  extremely  doubtful 
whether  or  not  there  is  a  true  nucleus.  The  coloring  matter,  instead 
of  being  confined  to  definite  bodies,  as  in  the  true  algae,  is  distributed 
throughout  the  cell  contents  or  forms  a  sheath  lining  the  wall  of  the 
cell. 
In  addition  to  the  simple  method  of  division,  certain  groups  of 
the  Schizophyceae  have  the  power  of  forming  thick-walled  spores, 
and  it  is  by  means  of  these  cells  that  they  are  able  to  tide  them- 
selves over  adverse  conditions  which  it  would  be  impossible  for  their 
vegetative  cells  to  withstand.  Thus  it  is  that  a  form  which  has 
once  existed  in  a  pond  or  stream  may  disappear  for  several  years, 
and  then  suddenly  make  its  appearance,  because  the  spores  made  by 
the  plants  in  the  first  place,  having  remained  in  the  mud  at  the  bot- 
tom, reach  maturity,  and  the  combination  of  temperature,  nutrition, 
etc.,  are  favorable  for  germination.  The  conditions  most  favorable 
for  the  rapid  increase  of  the  blue-green  forms  are  shallow,  stagnant 
water  and  relatively  high  temperature.  Consequently  it  is  during 
the  summer  months  that  the  most  trouble  and  annoyance  is  expe- 
rienced from  these  forms.  The  well-known  "  pig-pen  "  and  "  grassy" 
odors  are  given  off  and  water  supplies  rendered  quite  unfit  for  use 
by  the  unpleasant  odor  and  taste.  Jackson  and  Ellms  have  shown 
that  these  odors  are  due  to  the  breaking  down  of  highly  organized 
compounds  of  sulphur  and  phosphorus,  and  to  the  unusually  large 
amount  of  nitrogen  which  these  plants  contain. 
As  usually  classified  by  botanists,  the  Schizophyceae  are  divided 
into  two  groups,  the  Coccogoneae  and  Hormogoneae,  according  to 
whether  the  plant  consists  of  a  single  cell  or  a  number  of  cells.  The 
Hormogoneae  are  further  distinguished  by  the  power  they  possess  of 
breaking  their  filaments  up  into  smaller  groups  of  cells  called  hor- 
mogonia,  which  may  divide  rapidly  and  give  rise  to  new  plants. 
The  only  genera  among  the  unicellular  group  which  are  likely  to 
ciuse  trouble  are  Caelosphceri'im  and  Clathrocystis.    These  are  quite 
