^LA^'T STKUCTURES 



the food wliicli, 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. 



58. Symbionts. — 

 Symbiosis means 

 "living together," 

 and two organisms thus related are called S7jmlio7its. In 

 its broadest sense symbiosis includes any sort of depend- 

 ence between living organisms, from the vine and the tree 



Fig. 75. 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. 



