JuLy, 1915.] THE ORCHID REVIEW. 197 
into contact laterally, and soon begin to fuse. The fusion starts at the 
pointed colourless ends, and after these parts are quite joined up laterally 
the opposite ends remain for a short time separate. In a few minutes 
fusion becomes complete, and the two cells now constitute a single four- 
ciliated body, essentially different from the vegetative zoospore. The new 
body is called a zygospore, to indicate its origin from two united sexual 
cells, while the sexual cells are called gametes to indicate their special 
property of uniting. The origin from two united cells can long be 
recognised by the presence of two chlorophyll-bodies and two eye-like spots, 
one from each of the uniting cells. 
Movement does not continue long after fusion is complete. The 
zygospore withdraws its four cilia and comes to rest, attaching itself, like 
the vegetative zoospore, by the colourless pointed end. It now acquires a 
cell-wall, and often puts out a colourless root-hair by which it attaches 
itself to the substratum. Development now proceeds; the cell contents 
become darker and of a dark green colour, while the cell-wall is thickened, 
after which the new individual enters into a state of rest. After remaining 
dormant for a time the resting zygospores again become active, and the 
contents now break up simultaneously into a number of free cells or 
zoospores, from which the Ulothrix filament is again produced, and the life 
cycle is complete. It is interesting to note that if for any reason the two- 
ciliated gametes fail to conjugate they can germinate on their own account, 
either behaving like the asexual zoospores or forming resting spores like the 
zygospores. This indicates the important fact that the conjugating cells 
have not yet become exclusively adapted to a sexual function. There is also 
the remarkable resemblance of the sexually-produced zygospore to the 
vegetative zoospore, even to the restored size, and in the similar number 
of cilia. 
In Spirogyra, a fllamentous floating Alga, reproduction takes the form 
of a remarkably simple process, a form of conjugation between cells of 
adjacent filaments. These cells produce lateral out-growths, which come 
into contact and adhere together; the intervening cell walls are then 
absorbed, and the contents of one of the cells contract, and after a time 
The two nuclei then fuse together, and 
passes over into the adjacent cell. 
ounds itself with a new cell wall, and in 
the united protoplasmic mass surr 
due time gives birth to the new generation. The conjugating cells are 
alike, but one is the receptive one, and there are other indications of a 
certain degree of sexual differentiation. Vegetative reproduction takes the 
form of an occasional breaking up of the filament into its constituent cells. 
In many other members of the Conjugate there is no trace of any 
difference of sex, for the cells meet and fuse midway between the parent 
cells, each of which takes an equal part in the process. 
