THE: .MAIN » LINE. “OF » DESCENT 
THROUGH THE’ GREEN ALG 
By Grorce LUNAM. 
(Read roth December, 1912.) 
WITHIN recent years much work has been done in elucidating 
the inter-relationships of the Chlorophycez, and in the follow- 
ing pages a somewhat popular account is given of what may 
be regarded as the main line of plant descent, so far as it lies 
among these lowly forms. Almost at the foundations of the 
vegetable kingdom are a few groups of motile organisms back 
to which several lines of descent have been traced. The forms, 
however, that give us the starting point that seems to lead to 
the line ending in the higher plants belong to a very simple 
unicellular genus, Chlamydomonas (figs. 1 and 2), a few species 
of which are common in our area. Chlamydomonas, a walled 
unicell, as the name implies, contains a somewhat basin-shaped 
or bell-shaped chloroplast, has an eye-spot, a pair of equal 
cilia by which it moves about in the water where it is fonnd, 
and a pair of contractile vacuoles. When reproduction is 
about to take place the cell comes to rest and divides up into 
two to eight daughter cells which on liberation become new 
individuals ; sometimes the cell divides into as many as sixty- 
four, but these (gametes) on liberation fuse in pairs, giving 
rise to zygospores which produce new individuals. Some 
species under suitable conditions enter a stage known as the 
“palmella state”; and others seem to be mainly in this condi- 
tion—a resting period in which the cells have lost their cilia 
and are embedded in mucilage derived from the cell wall 
(fig 3.) 
The emphasising of this condition by the adoption of a 
vegetative mode of increasing the number of resting cells has. 
probably led on to the higher developments shown in the 
Chlorophycex. It is from this simple organism in its motile 
state that the evolutionist readily traces a very clearly marked 
