86 



PLANT STEUCTUEES 



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 Algffi 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. — 

 The phenomenon of 

 symbiosis has already 

 Lichens (§ 53). In 

 any sort of drpcnd- 



FlG. 75. A dodder plant parasitic on a willow twig. 

 Tlie leaflL'tsy dodder twines al)Out the willow, and 

 sends out sucking processes which penetrate and 

 ahsorh.— After Steasburgeb. 



been referred to in connection with 

 its broadest sense the word includes 

 ence between living organisms, from the vine and the tree 



