482 LIFE-HISTORIES 
single nucleus and a chromatophore in the form of a nearly 
complete hollow cylinder. 
Eventually in some of the cells (B) the protoplasm assumes a 
spheroidal form or may divide into from two to eight smaller masses 
each provided with a nucleus through division of the original one. 
These globular masses soon begin to move and presently make their 
way into the surrounding water through an opening in the old 
cell-wall. When outside, however, they are still surrounded by a 
delicate cellulose membrane, but this soon ruptures setting free 
the naked protoplasts. Each of these (C) is now seen to be some- 
what pear-shaped, with a colorless pointed end from which come four 
slender lash-like projections, called flagella.1_ The rounded part is 
grass-green and contains a bright red granule termed the eye-spot. 
As soon as they are free, these naked protoplasts swim about with 
rapid motion, propelled by their lashing flagella. After a while they 
come to rest, secrete a cellulose wall, and germinate by fission, the 
lower one of the two cells first formed becoming the pseudo-root by 
elongation and attachment to the substratum, while the upper 
cell develops into a long green multicellular thread by repeated 
divisions. A naked motile protoplast, by means of which a plant 
is multiplied non-sexually we call a swarm-spore. Ulothrix repro- 
duces also by motile gametes in which may be discerned occasionally 
a slight inequality in size suggesting the beginnings of difference 
in sex although for the most part they appear quite alike. These 
sexual or subsexual gametes arise from the cells of the filament in 
much the same way as the swarm-spores do, but they are more 
numerous and smaller, and possess only two flagella (D, #). They 
unite sidewise (F) with their tips together, thus producing what 
looks like a swarm-spore (@), with its four flagella, but which differs 
in having two eye-spots. A protoplast resulting from the fusion of 
two protoplasts, whether they be alike or unlike, is termed a zygote.? 
The zygote of Ulothrix soon absorbs its flagella (H), becomes round, 
and secretes a cellulose wall, thus becoming a resistant zygospore 
ready for a period of rest. The zygospore germinates by forming 
several swarm-spores (K) each of which in turn grows into a thallus 
as already described. 
In the sheath algze (Coleochete) the thallus (Fig. 314), 
is in the form of a flat disk or cushion-like mass attached 
to some support by the lower surface. This disk as in the 
species figured usually consists of branching filaments which 
elongate by repeated division of the terminal cell and branch | 
by its frequent forkings. (B,a-g). In other species the fila- 
1Fla-gel’lum < L. a whip. 
2 Zy’gote < Gr. zygotos, yoked. 
