THE ALG 229 
Vauheria has three methods of reproduction — vegetative, 
by asexual spores (zodspores), and by sexual spores (odspores). 
One plant may use vegetative reproduction at one period 
of growth, asexual spore reproduction at another, and sex 
spore reproduction at another, but two methods are rarely 
used at the same time. 
215. Other green alge. Although 
in inland waters green alge are more 
abundant than all others, only two 
other genera will be mentioned in 
this connection. Spherre/la, a unicel- 
lular form somewhat like Plewrocaccus, 
is frequently found in stagnant water. 
It sometimes grows so luxuriantly in 
barnyard and roadside pools as to 
give the water a bright green appear- 
ance, and its resting spores may im- 
part a dark red color to diving pools 
in which the plants have flourished. 
Chara, or stonewort (fig. 179), is a 
complex alga that is found in great 
abundance on the bottoms of shallow 
lakes and streams throughout the ee ee ee 
continent. It has a heavy coating of a plant, showing the general 
calcareous material, which, as the maenifed Hl 2 ie heen eared 
plant dies, falls to the bottom of the the odgonium (0) and the an- 
pond or stream. Chara grows in such ei pene ts oe 
luxuriance that its deposits eventually 
form deep layers of this calcareous material, or marl, as it is 
called. Alarl has been found of great value as one of the mate- 
rials used in the manufacture of cement, and not a few of the 
lakes in which Chara grows are dredged to secure the marl 
deposits for this important manufacture. 
216. Alge and water supply. Many of our large cities have 
found it advisable to adapt or construct reservoirs for water 
supply. These are open pools, lakes, tanks, ete., and they are 
Fie. 179, The stonewort alga 
(Chara) 
