262 CHLAMYDOMONAS. 



stained the protoplasm, (2) the nucleus, (3) the starch 

 collected at the pyrenoid, (4) the cilia, (5) the cell- wall. 



(c) To some fresh Cklamydomonas add a drop of alco- 

 hol ; this kills the cell and extracts the chlorophyll. 



(d) In the scum-like deposit sometimes found in water 

 containing Chlamydomonas, the plant may be seen in what 

 has been called its " palmelloid " condition ; many other 

 simple Algae, however, pass at times into this condition. 

 The plant comes to rest, and loses its cilia, eye- spot, and 

 contractile vacuoles ; the cell-wall becomes swollen and 

 mucilaginous, and in the mucilage thus formed the cells 

 undergo active division, and thus multiply rapidly. Then, 

 with the return of favourable conditions for active motile 

 life, the cells escape, and the plant becomes motile again. 



(e) Some of the Chlamydomonas cells may also be seen 

 to have come to rest, withdrawn their cilia, and divided 

 into four daughter-cells, or zoogonidia, which later are set 

 free, each acquiring a pair of cilia, and form independent 

 plants like the parent. This is a simple example of asexual 

 reproduction. 



(/) The different species of Chlamydomonas differ considerably in 

 structure and in their modes of sexual reproduction. The chloro- 

 plast, instead of being simply bell-shaped, may be cut up into lobes ; 

 there may be four instead of two cilia. The greatest differences, 

 however, are seen in the sexual reproduction, which may be effected 

 by (1) the conjugation in pairs of equal-sized biciliate zoogametes, 

 wall-less (in rare cases walled) cells produced by repeated division 

 (to the number of as many as 32) of an ordinary cell and set free into 

 the water, the zygote formed by fusion often acquiring a thick coat 

 and resting before passing into the motile state again ; (2) the con- 

 jugation of smaller biciliate gametes (microgametes) with larger 

 ones (megagametes) ; or (3) the fertilisation of a large walled cell 

 by a smaller one. That is to say, we find in this genus a gradual 

 transition from isogamy to heterogamj 1 -, the gametes being in the 

 former case similar in size and in the second case dissimilar. 



(ff) It has been shown that the plant only reproduces asexually 

 when cultivated in Knop's solution, but when transferred from 

 this to distilled water it soon produces zoogametes, which fuse in 

 pairs to form zygotes. If a single zoogamete is isolated in some dis- 

 tilled water it perishes ; but if it be isolated in culture solution it 

 will give rise to a new individual i.e. it will behave in the same 

 way as a zoogonidium. Such experiments, which are more readily 

 performed with larger Algae, and also with Fungi, show that the 



