78 
F. Cavers. 
RECENT WORK ON FLAGELLATA AND 
PRIMITIVE ALG/E. 
By F. Cavers. 
(Continued from p. 36j. 
IV.— Relation of Green Alg^e to Chlamydomonads. 
T HERE appears to be strong support for the view that the 
majority of the Green Algae may be derived from Flagellate 
ancestors with two or more equal flagella. In 1897, Chodat (24) 
pointed out that in the life-history of the lower Green Algae there 
may be distinguished three conditions, either of which may become 
dominant, the other two being then transient or suppressed : (i.) the 
zoospore condition or motile stage; (ii.) the sporangium condition 
or unicellular motionless stage; (iii.) the palmelloid condition, in 
which non-motile cells are connected into aggregates by cell-walls 
at right angles to each other. In 1900, Blackman (6) published an 
important paper on the phylogeny of the Algae, containing not 
merely a critical summary of modern work bearing upon the 
problem, but also various far-reaching suggestions as to the lines 
along which the evolution of the different Algal groups may be 
traced from Flagellata. Blackman pointed out that among the 
simple Green Algae which constitute the group of Protococcoideae 
three divergent vegetative tendencies are observed : (i.) a Volvocine 
tendency towards the aggregation of motile vegetative cells into 
gradually larger and more specialised motile ccenobia ; (ii.) a Tetra- 
sporine tendency towards the formation of aggregations by the 
juxtaposition of the products of septate vegetative cell-division to 
form non-motile organisms of increasing definiteness and solidarity; 
(iii.) an Endosphasrine tendency towards the reduction of vegetative 
division and septate cell-formation to a minimum. The simplest 
forms showing any one of these tendencies seem clearly to diverge 
from species of the genus Chlamydomonas, which may be regarded 
as the phylogenetic starting-point of the various lines of Green 
Algal descent. The line arising from the Volvocine tendency leads 
to the Volvocales and culminates in Volvox; the outcome of the 
Endosphaerine tendency is seen in the Siphoneae ; while the Tetra- 
sporine line has given rise to the great majority of the Green Algae 
and through these to the Archegoniatae and other higher plants. 
The phylogeny of the Conjugatae, GEdogoniales, and a few other 
isolated groups of filamentous Green Algae remains in some doubt, 
owing to the absence of undoubted transitional forms connecting 
these groups with either the Tetrasporine line on one hand or with 
distinct Flagellate ancestors on the other. For further details 
regarding the phylogeny of the Green Algae, reference should be 
made to the paper by Blackman already mentioned (6), and to the 
