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 Salvinia, of Gunnera manicata, 
D 
H 
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, 
