96 



BOTANY 



spot (eye-spot), like that found in some Flagellata. Occasionally 



(e.g. Chlorogoniuin) there 

 may be several chromato- 

 phores, and in the genus 

 Chloraster there are five 

 cilia. 



Movements. The Vol- 

 vocacese are actively mo- 

 tile, and the movements 

 are strongly influenced by 

 light. The eye-spot is 

 with little question con- 

 nected with this sensi- 

 tiveness to light. In the 

 multicellular forms, the 

 cells about the forward 

 pole of the globular cell- 

 family have the eye-spot 



much better developed 

 FIG. 67. A,. Sphxrellapluvialis, active individual ,, ,, ,, f ,, 



(X300). B, conjugating gametes (X750). tnan 

 V, cells of Volvox minor, showing protoplas- hinder pole. 



The lower Volvocaceae 



mic connections, and a young antberidium, 6 



(X 500). D, section of egg-cell of Volvox minor, <1 >. 11 



showing the large central nucleus, and the e ~9- & P n 



peripheral chromatophore containing numerous Chlamydomonas, are 



pyrenoids (X550). E, a spermatozoid (x700). strictly unicellular, but 



(A, B, after BLOCHMANN ; D, .E, after OVERTON.) ,, ,, 



the most or genera are 



cell-aggregates of definite form. "The number of cells ranges from 

 sixteen in Gonium to several thousand in the genus Volvox. 



Classification of Volvocaceae 



The Volvocaceae may be divided into three families: Chlamydomonadinse, 

 Phacotese, and Volvocese. The first two comprise unicellular forms, the latter 

 are all multicellular. 



Chlamydomonadinae. In the Chlamydomonadinse the unicellular free-swim- 

 ming cells may withdraw their cilia and assume a non-motile condition in which 

 they are capable of repeated fission, giving rise to large colonies of non-motile 

 cells which closely resemble certain Protococcoidese, from which they are scarcely 

 distinguishable. Sphcerella nivalis, the "Red-snow" plant, is an example of 

 this. In this plant, as well as in the spores of other Volvocacese, the red pig- 

 ment haematochrome is present. These non-motile cells, however, may escape 

 from their gelatinous matrix and resume their active form. Gametes are formed 

 by internal division of the cell, these being either quite similar or slightly dif- 

 ferent in size. The cell formed by their union becomes a resting-spore whose 

 contents finally divide into several (2-4) parts, each of which escapes as a free- 

 swimming cell. 



Phacoteae. The Phacotese include a small number of unicellular forms 



