374 BOTANY OF THE LIVING PLANT 



passes through the oesophagus, and is attached by a branched base 

 to the inner surface of the vacuole. In this state Euglena can feed 

 itself b}?- photo-synthesis, but it probably obtains simultaneously 

 some degree of saprophytic supply from the foul water in which it 

 lives. When well nourished it may contain large paramylum bodies, 

 but not starch. It multiplies by fission, the nucleus dividing 

 first (Fig. 315). When starved for a lengthened period an encysted 

 form is assumed. The chromatophores diminish in size and colour, 

 and storage materials appear in the contracted protoplasm, which is 

 then surrounded by a thick wall (Fig. 314,/)). In this state it can resist 

 conditions that are adverse. But when these are favourable again 

 the cyst germinates ; its wall becomes mucilaginous ; the 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 (£). No sexual process has been observed 

 in Euglena, though certain Flagellates show conjugation. 



The common Eugle^ia viridis does not grow well in spring water, 

 but it flourishes in water containing organic impurities. Probably 

 photo-synthesis 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 according 

 to circumstances. Fig. 314, 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 w^hich show characters so versatile suggest several distinct 

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

 would give rise to features characteristic of the largest groups of 

 living beings. The motile green condition, with the capacity for 

 photo-synthesis, if it becomes encysted, loses its motility while it 

 achieves protection. The encysted form of Euglena after division 

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

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

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

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

 Plants. But the protoplasts of Euglena may soon escape and 

 become motile again, a condition which is seen repeated commonly 

 in the propagative cells of Plants up to the Gymnosperms. Thus the 



