PHYLOGENY 



phyll is confined to cell organelles, the plastids, but that of the blue-green 

 algae is diffusely spread throughout the outer part of the cell. Their bluish 

 color is caused by a blue pigment, phycocyanin, and a red pigment chemi- 

 cally similar to that of the red algae may also be present. Unlike most 

 other algae, they lack flagella, and are in fact generally non-motile. The 

 oldest known fossils, from rocks on the order of a billicm vears old, are 

 remains of blue-green algae, and their descendants of todav are regarded 

 as little-changed survivors from that remote time. Whether other groups 

 of algae have been derived from blue-green ancestors is unknown, but the 

 fact that the blue-green algae share with more advanced groups so funda- 

 mental a trait as the possession of chlorophyll at least indicates that this 

 is a possibility. 



THE EUGLENOPHYTA AND THE SEPARATION 

 OF THE KINGDOMS 



The Euglenophyta, typified by the common Euglena of elementary biol- 

 ogy laboratories, show many advances over the blue-green algae. They 

 have a definitely organized nucleus which is separated from the cytoplasm 

 by a membrane. The chlorophyll is no longer free in the cytoplasm, but 

 rather it is concentrated in numerous ovoid bodies, the chloroplasts. Fur- 

 ther, the color is grass-green rather than blue-green. Unlike the green 

 algae, the Euglenophyta are not provided with a cellulose cell wall. The 

 cells are provided with one or two flagella, and they are active swimmers. 

 There is a gullet at the anterior end, yet it appears that Euglena is auto- 

 trophic. Near the gullet there is a red pigmented eyespot, which seems 

 to be sensitive to light. Reproduction is always by simple mitotic division, 

 although sexual reproduction has been reported for one genus (Scyto- 

 monas). 



The Euglenophyta are also described in zoological works as the order 

 Euglenoidina of the class Flagellata and the phylum Protozoa. This class 

 includes representatives of most of the unicellular algal phyla as well as 

 some indisputably animal flagellates. The group as a whole shows a curi- 

 ous mixture of plant and animal characteristics. 



But before taking up this subject, it may be well to consider what are 

 the typical differences between plants and animals. Generally speaking, 

 the mode of life of animals is aggressive, while that of plants is passive. 

 Animals are heterotrophic, eating other organisms to obtain the complex 

 organic compoimds which they require as foods. Plants, on the other 

 liand, are generally autotrophic, being able to synthesize all of their food 

 requirements from the elements. But there are exceptions in both king- 

 doms. Many of the higher plants, such as the sundew (Drosera), have 

 developed mechanisms for the capture and digestion of insects, and many 

 animals are saprozoic, that is tliey absorb decaying organic matter from 

 their environment. In plants, differentiation of organs is predominantly 

 external, while in animals it is predominanth' internal. In plants, growing 

 tissue, the meristem, is present at all stages of tlie life c}'cle, whereas most 

 animals have a definitely limited growth. Finally, plants are generally 



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