240 
Welsford . — The Morphology of 
consist of several cells ; the basal ones contain chlorophyll, and the rest 
are colourless. The ordinary branches of the thallus arise as outgrowths 
immediately behind a septum. The hairs develop in a very similar way, 
but usually grow out from the middle of a lateral wall. The presence of 
protoplasm in every cell of the hair was clearly demonstrated in prepara- 
tions stained with brazilin, and it seems probable that these hairs are really 
slightly modified branches. 
The vegetative cells of the disc and branches contain a large parietal 
chloroplast with irregular lobes, a nucleus, and a pyrenoid. 
Reproduction. In young plants any cell is capable of producing 
zoospores, but as development proceeds a certain amount of differentia- 
tion takes place. The most common reproductive organs at this stage 
are large sporangia, which may be either terminal or intercalary, and 
which are always characterized by deep coloration. They generally 
occur in groups, and the various successive stages by which the contents 
of the sporangium divide into eight portions may often be found close 
together. The mature sporangium measures about 16 x 12 j a, and contains 
eight gametes which are set free through a pore or pores in the wall. 
When first liberated each gamete measures about 3 //, in length, but quickly 
becomes 6 /x, and shows a distinct eye-spot and two equal cilia ; the 
zoospores soon fuse in pairs and come to rest. The interval of time 
between fusion and germination was not determined, but some of the 
stages of germination were studied. 
The zygote at an early stage appears to be firmly fixed to the sub- 
stratum ; a branch grows out from one end of it and is cut off by a cell-wall. 
As soon as this cell has developed into a short filament, another branch 
usually grows out from the opposite end of the zygote. Occasionally 
a zygote germinates at both ends simultaneously. The first-formed 
filaments grow rapidly, branch, and develop into the characteristic thallus. 
In many cases zygotes were found germinating so close to one another 
that their filaments combined together to form one plant or colony. 
Sometimes the contents of the sporangium fail to form gametes, and 
while still within the cell-wall divide to form a filament of from 2 to 8 cells. 
The wall of the sporangium eventually ruptures, setting free the young 
plant. Occasionally cases were found in which the sporangium ruptured 
after the first division and liberated two non-motile daughter-cells which 
were capable of germination. 
Besides these large sporangia, groups of smaller ones are found on 
poorly developed filaments. They measure about 6x4^ and contain from 
8 to 16 motile cells which are liberated through an opening with a definite 
lid, which, however, is quickly lost. Owing to their small size and rapid 
movement their further development was not satisfactorily studied. Some- 
times the contents of these small sporangia were liberated after one or 
