86 



PLANT STRUCTURES 



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. 



58. Symbionts. — 

 Symbiosis means 

 " living together," 

 and two organisms thus related are called symbionts. 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 Strasbubger. 



