EXERCISE 26 



HOW DO PLANTS WITHOUT CHLOROPHYLL SECURE THEIR 

 FOOD? A PARASITE AS AN EXAMPLE 



Materials. Common dodder (Cuscuta), which may be found as a 

 field pest and on wild plants in many parts of the country. Other 

 dependent flowering plants may be substituted if more convenient, 

 but in this case the directions must be suitably modified. Mistletoe, 

 beechdrops, broom rape, pinesap, and cancer-root are examples of 

 parasites ; Indian pipe is a saprophyte. The class should study the 

 material in the field if possible. 



Directions for work. Describe the general characteristics of 

 the dodder plant, such as its size, color, presence or absence of 

 leaves, and manner of climbing. 



What evidences of a dependent habit do you find in the struc- 

 ture, color, etc. of the dodder ? What evidences of a parasitic 

 habit in its connection with the host? Cut sections through 

 host and parasite and by a study of these determine whether 

 the parasite penetrates the host or is merely adherent to the 

 outside. What evidence do you see of any effect of the parasite 

 on the host? 



References 



BERGEN and CALDWELL. Practical Botany, pp. 383, 384. 

 BERGEN and CALDWELL. Introduction to Botany, pp. 51-53. 



[30] 



