SAPROPHYTISM AND SYMBIOSIS 



341 



semi-parasitism is that of the blue-green alga, Nostoc, 

 species of which grow in little pockets or cavities in the 

 tissues of the water-fern Sahinia, of Gunner a manicata, 



FIG. 249. Photomicrograph of a cross-section of the stem of a dicoty- 

 ledonous host-plant infested with the parasite, dodder (Cuscuta sp.). 

 Note the haustoria extending from the dodder (D, D') into the cortex of 

 the host (H). Greatly enlarged. 



of Anthoceros, and of other plants, without apparent 

 injury to the host (Fig. 160). 



312. Artificial Parasites. By recent experiments cer- 

 tain plants have been induced, by experimental treatment, 



