192 SEAWEEDS 
ever, been established by direct observation, is the 
fact that most of the Diatoms possessing such a 
power of movement possess also longitudinal sutures, 
and it is supported by the observation that fine 
particles of matter (not motile by themselves) sus- 
pended in the water, on coming in contact with the 
membrane, are set in motion along the suture. 
However, no one has so far demonstrated the pro- 
trusion of any protoplasm at this place. That these 
movements take place with considerable relative 
force is shown by the observation of Donkin, who 
saw one species push away another at least six times 
its size, while other observers state that they have 
seen this greatly exceeded. The speed of the move- 
ment when compared with the rapid dartings of 
ciliated organisms is slow. The Rev. William Smith 
estimated the rate at about four hundred times a 
Diatom’s length in three minutes. 
eproduction.—Diatoms multiply by successive bi- 
partitions. The actively vegetating cell increases 
slightly in volume, and the two valves are slowly 
pushed out until the overlapping girdle remains in 
that position, but no more. The protoplasm then 
divides into two, and two daughter-cells are formed, 
not separated by a membrane in the ordinary way, 
but each new cell forms a new valve on the plane of 
division. The edges of the new valves fit into the 
girdle of the old valves of the parent cell, and these 
old valves overlap the new ones. Each daughter- 
cell thus possesses two valves, one newly formed and 
overlapped by the old one. The cells either separate 
and become free, or they remain in contact, and 
