SPIROGYRA 225 
parent cell. This, surely, is a case of “‘ wheels within 
a wheel.” In time the parent cell breaks up, 
setting free the enclosed cells, which become full- 
sized, and in their turn give harbourage within 
themselves to new cells. 
Before we set aside the microscope, I want to 
examine the green, scumlike conferva that I 
gathered to-day. 
As I expected, we have specimens of the green 
Alga called Spirogyra. This weed is a very lowly 
plant. It grows in threadlike lengths, which may 
be less than an inch in extent, or upwards of a yard. 
In running streams it may be seen hanging from 
weeds in long streamers, but in still waters it grows 
independently, and appears like a kind of scum. It 
may be got in cattle-troughs by the roadside—in 
fact, almost anywhere where water is allowed to 
stand for any time. Each thread is composed of a 
number of single cells placed end to end. Under 
the microscope, as you observe, the chlorophyll, or 
colouring matter, appears to be arranged in delicate 
spiral bands which are rough on the edges. Each 
band is relieved by frequent spots of a brighter 
green, and in each cell a central body, or nucleus, of 
living matter is evident. 
We have been fortunate enough to secure two 
threads of Spirogyra in what is called a state of con- 
jugation. You see them quite distinctly. The two 
threads have come together ; the cells have put out 
little processes by which the threads have joined, 
and the joined processes look almost like the rungs 
of a ladder. In these threads the cell contents have 
lost their ordinary appearance; the chlorophyll 
29 
