158 
PLANT STUDIES 
the food which they manufacture. The less chlorophyll is 
used the less is it developed, and a green plant which is 
obtaining the larger amount of its food in a saprophytic 
or parasitic way is 
on the way to losing 
all of its chlorophyll 
and becoming a com- 
plete saprophyte or 
parasite. 
Certain of the low- 
er Algae are in the 
habit of living in the 
body cavities of high- 
er plants, finding in 
such situations the 
moisture and protec- 
tion which they need. 
They may thus have 
brought within their 
reach some of the 
organic products of 
the higher plant. If 
they can use some of 
these, as is very like- 
ly, a partially para- 
sitic habit is begun, 
which may lead to 
loss of chlorophyll 
and complete para- 
sitism. 
121. Symbionts. 
The phenomenon of 
symbiosis will be re- 
ferred to more fully in connection with Lichens ( 194). 
In its broadest sense the word includes any sort of depend- 
ence between living organisms, from the vine and the tree 
FIG. 148. A dodder plant parasitic on a willow twig. 
The leafless dodder twines about the willow, and 
sends out sucking processes which penetrate and 
absorb. After STRASBURGER. 
