172 



Volvocineae 



The palmella-state can be directly induced by cultivating Chlamydomonas in nutritive 

 solutions or on more or less solid media. It is probable that some of the described species 

 of Gloeocystis, such as Ol. vesiculosa Nag., are merely the palmella-states of species of 

 Chlamydomoii as. 



A vegetative resting-state has been found to occur in certain species 

 (Chi. alpina, Chi. gigantea, Chi. nivalis, etc.) and Wille ('03) has suggested 

 that several of the described species of Trochiscia (= Acanthococcus) are 

 merely the resting-cells (akinetes) of Chlamydomonads. There is, however, 

 as yet no definite proof of this. 



Planogametes are known to occur in a number of the species ; they are 

 in all cases similar to the vegetative cells (= zoogonidia), but smaller and 

 are produced up to 64 in the mother-cell. They are generally naked, but in 

 some species they may be clothed with a cell-wall (Chi. media Klebs ; fig. 92 

 and H). In most cases the gametes are isogamous, but in some species 

 heterogametes (anisogametes) occur, and in Chi. monadina Stein the conjuga- 

 tion of the gametes is a case of true oogamy, the contents of the megagamete 





J 



Fig. 101. A F, Brachiomonas sitbmarina Bohlin ; A and B, side views of vegetative individuals 

 (zoogonidia) ; C, anterior view ; D, formation of four zoogonidia (daughter-cells) within old 

 inother-cell-wall ; E, gamete ; F, zygote. G and H, Phacotus lenticularis Stein, two views 

 showing compression of cell. I, Lobomonas stellata Chodat ; J, Lobomonas Francei Dang. 

 n, nucleus ; py, pyrenoid ; r, vacuole. A F, x 1000 ; G and H , x 800 ; I, very highly 

 magnified (after Chodat) ; J, x 1000 (after Dangeard). 



acting as an egg-cell (fig. 100 1 3}. The zygote often exhibits distinct 

 specific characters, being adorned with short spines, warts, etc., or variously 

 sculptured. 



'This genus {.Chlamydomonas] holds a unique position among the Green Algae, and 

 indeed among the whole of the Green Plants. It may lie regarded as the phylogenetic 



