358 BOTANY OF THE LIVING PLANT 



contents usually divide into two or four (E. gracilis), or even more parts 

 (E. viridis), which, after showing movement within the wall, are finally 

 set free as naked protoplasts (E.). Some Flagellates show sexuality ; 

 this has been noted also for Euglena, but needs confirmation. 



The common Euglena viridis does not grow well in spring water, 

 but it flourishes in water containing organic impunities. Probably 

 photosynthesis is its chief mode of nutrition, but it can also act as a 

 partial saprophyte. This is more clearly seen in E. gracilis, which 

 has been shown to be either autotrophic or purely saprophytic accord- 

 ing to circumstances. Fig. 265, C, shows the colourless form grown in 

 the dark in a nutritive medium. The chromatophores are reduced 

 to small pale plastids, but still the organism appears well nourished. 

 This saprophytic type can then be restored to the autotrophic condition 

 by exposure to light. It thus appears that certain Flagellates may 

 temporarily or permanently make use of a saprophytic mode of 

 nutrition. 



Organisms which show characters so versatile suggest several distinct 

 lines along which evolution is possible ; and those lines if realised 

 would give rise to features characteristic of the largest groups of 

 living beings. The motile green form with the capacity for 

 photosynthesis, if it becomes encysted, loses its motility while it 

 achieves protection. The encysted form of Euglena after division of 

 its protoplast is so like certain Algae allied to Palmella that it has 

 been called the " Palmella- state" The resulting cells remain grouped 

 for a time. If that state became permanent, and the divisions 

 numerous, a cell-colony would be formed of a type characteristic for 

 certain simple types of Plants. But the protoplasts of Euglena may 

 after division escape and become motile again as primordial, that is 

 naked cells, a condition which is seen repeated commonly in the 

 propagative cells of Plants up to the Gymnosperms. Thus the 

 encysted state of Euglena suggests a possible mode of initiation of the 

 encysted construction characteristic of Plant-Forms (compare Chapter 

 X.). But most of them still retain the primitive primordial cell in 

 reproduction. 



The saprophytic mode of life in Euglena — or parasitic, as it is in 

 many other Flagellates, which are then independent of light and 

 chlorophyll — suggests a distinctively animal existence. Here motility 

 is retained, and encystment appears only as an occasional incident. 

 This behaviour of Euglena, an organism in which sexuality has 

 not hitherto been verified fully, indicates that the segregation of 

 Animals and Plants may have antedated sexuality. But such ideas 



