38 EVOLUTION OF PLANTS 



the higher plants. These are known as the Volvoca- 

 cea;, or Volvocinese, and have been claimed by zoolo- 

 gists as animals, although there seems no question of 

 their close relationship with the lower green plants. 

 It is true that they are actively motile, and show other 

 animal properties, but they usually possess a cellulose 

 membrane, and the characteristic green chromatophore 

 of the typical plant cell, and inasmuch as they are con- 

 nected with unmistakable plants by a complete series 

 of intermediate forms, there seems to be no valid 

 reason for not considering them as low plants. It 

 is interesting to note, however, that the lower mem- 

 bers of the series of Volvocinese are very much like the 

 animal flagellate infusorians and also the swarm-spores 

 of the slime-moulds, from which they differ mainly in 

 the presence of a green chromatophore. The frequent 

 recurrence of this free-swimming, flagellate type among 

 both the lower animals and plants suggests some similar 

 forms as the ancestral type for both of the great series 

 of organic beings, which here converge. 



The siniplest of the Volvocineae are round or oval 

 cells, which in their ordinary condition are actively 

 motile,| swimming by means of two delicate cilia. In 

 the younger stages these cells are quite destitute of a 

 membrane, but older cells usually have a distinct cellu- 

 lose wall, with openings through which the two cilia 

 protrude. The structure (Fig. 6, B) is that typical 

 of the lower green plants. The green chromatophore 

 (chloroplast) has the form of a cup and fits into the 

 lower part of the oval cell-cavity. Within the hollow 

 of the chromatophore is included a mass of protoplasm 

 in which is imbedded the nucleus. The forward end 



