The Lower Plants 51 



plants and animals than do any other existing or- 

 ganisms. The flagellates were long looked upon as 

 a division of the Infusoria, the most important 

 group of unicellular animals, but recent studies on 

 these forms have shown that there are two well- 

 marked types, one of which possesses the chromato- 

 phores or chlorophyll-corpuscles characteristic of 



FIG. 3 



A colorless flagellate, Bodo caudatus, attacking a flagellate 

 unicellular plant, Chlamydomonas, which possesses a green 

 chromatophore, cr. A nucleus, n, is present in each organism. 

 (After Butschli.) 



the typical plants, while in the others the chromato- 

 phores are wanting. All flagellates possess cilia 

 or flagella, by means of which they are propelled 

 through the water. The green flagellates closely 

 resemble many of the lower green plants, which 

 often give rise to free swimming reproductive cells 

 very closely resembling these flagellates and sug- 

 gesting that the latter are related to the ancestors 

 of the higher green algae. On the other hand, the 



