Laminaria digitata arid Laminaria saccharina. 185 
origin of the flagella, and in this stage the similar flagella of each gamete 
point in opposite directions. Later stages in conjugation were observed in 
which partial fusion of the gametes had occurred, with retraction of the 
flagella, and from this stage the formation of the spherical non-flagellated 
zygospore was traced. 
The whole process of conjugation, from the first meeting of two 
gametes to the formation of the zygospore, takes some hours. I was never 
able to keep any two particular gametes under the field of view for a 
sufficiently long period to watch the complete process in the case of the 
same two gametes, but I observed so many stages of fusion on so many 
different occasions that no possibility of doubt of the occurrence of true 
isogamous conjugation is left in my mind. 
After conjugation, the resulting zygospore was found in the culture 
as a colourless, non-flagellated, body, situated on the bottom and sides of the 
vessel, mostly in the focus of the light (Fig. 5, e). About twelve days after 
inoculation, a clear tube with a rounded end grows out, the rounded end 
expands, becomes spherical, and soon equals the zygospore in size. The 
protoplasmic contents of the parent cell then pass down the tube, 
eventually leaving an empty case behind. This in time degenerates and 
becomes separated (Fig. 
This body now forms chromoplasts, and increases in size. During 
growth the first formed chromoplasts subdivide, and an outer and inner cell- 
wall are formed (Fig. 5, z, /). When the cell has reached a diameter of 
about -025 mm., division occurs, and a chain of cells is formed, each show¬ 
ing an outer and an inner cell-wall. In some cases division results in 
an aggregated mass of cells, but typically a chain is formed (Fig. 6). 
This stage will in future be alluded to as the ‘ sporophyte 1 (see p. 188). 
In from six to eight weeks after inoculation, many of the cells of the 
sporophyte develop a bulging protuberance. The outer cell-wall then 
ruptures at the apex of the protuberance, and the contents of the spore, 
enclosed in the inner cell-wall, partially emerge. This cell then starts active 
division, and forms the characteristic thallus of the young Laminaria plant. 
After a few divisions, the young thallus shows differentiation into a flat 
lamina, consisting of roughly cubical cells containing chromoplasts and 
a number of colourless unicellular rhizoids, which are each attached to one 
of the basal cells of the lamina. The rhizoids are at first enclosed within 
the ruptured outer cell-wall, which appears somewhat flask-shaped, and has 
colourless transparent walls and a circular opening at the neck. In time 
this outer coat degenerates, and the rhizoids become attached to surrounding 
objects (Fig. 6). 
During this development of the rhizoids, the cells of the lamina are in 
a state of active division. They form parallel rows, one cell thick, in 
a direction at right angles to the long axis of the lamina. The number of 
