PHANEROGAMOUS PARASITE AND ITS HOST 249 



317. Relations of a Phanerogamous Parasite and its Host. Secure 

 a number of seeds of Cuscuta in the autumn and keep in a cool 

 place until needed in the experiment room. Germinate a number 

 of seeds of Helianthus, or Impatiens, in a pot filled with soil and 

 when the shoots have reached a few cm. in height sow the seeds 

 of Cuscuta in the soil around the plants. Note the behavior of 

 the seedlings of Cuscuta. After a time the parasite will coil 

 around the host plant and attach itself by means of special out- 

 growths, the haustoria. Examine the structure of these. Cut 

 cross sections of the stem of the host at points penetrated by the 

 haustoria and note their action. The anatomical relations of the 

 two plants may be seen if material is taken in August and pre- 

 served in alcohol, or formalin until needed, although this plant 

 offers an easy demonstration of the stimuli serving to direct the 

 parasite in its attachment to a host. Test the stem of Cuscuta for 

 chlorophyl (184). 1 Examine also plants of Epiphegus, Phora- 

 dcndron, Arceuthobium, or any convenient parasite and note the 

 effects of the parasitism on host and parasite. 



1 Peirce, G. A contribution to the physiology of Cuscuta. Annals of Botany, 

 8: 53. 1894. 



Mirande. Recherches physiologiques et anatomiques sur les Cuscutacees. Bull. d. 

 Sc. d. France et d. 1. Beige. 25: 1900. 



