282 MR. C. DARWIN ON THE ACTION OF 
Spirogyra (crassa ?) — When filaments of this alga were placed 
in a solution of earbonate of ammonia (4 to 1000), the cell-sap 
became in a few minutes cloudy from the formation of innume- 
rable granules, and the green spiral ehlorophyll-band soon began 
to contract. A filament was irrigated under a cover-glass at 
11.10 a.m. (Oct. 4) with the solution; and by 11.25 the cell-sap 
had everywhere become granular: in two of the cells the pointed 
ends of the chlorophyll-band and the irregular lateral projections 
were retraeted, so that these bands now appeared much smoother 
and blunter than before. In two neighbouring cells the bands 
had become converted into circular masses surrounding the 
nuclei. 
At 12.50 two cells were selected for further observation: in 
one of them the original spiral band now formed a layer of 
nearly uniform thickness, except in three of the corners where 
there were rounded lumps, which adhered closely to the two 
transverse and to one of the longitudinal walls of the cell. By 
4 p.m. the layer on the longitudinal wall had become in the 
middle so thin that it consisted of a mere thread, which at 4.15 
broke and disappeared; the upper end (with reference to the 
observer) of the layer then rapidly contracted into a pear-shaped 
mass. The layer at the lower end of the cell had by this time 
assumed a dumb-bell shape, which, however, soon afterwards 
became cylindrical. At 7.10 p.m. the appearance of the cell was 
utterly different; for there were now at the upper end two ill- 
defined masses, and at the lower end two somewhat irregular 
balls of green matter connected together by a thin band. At 
8 A.M. on the following morning there was a large oval mass 
lying obliquely across the upper end of the cell, with its two 
extremities connected by bands with two spheres in the lower 
corners. 
The changes in the other cell, which was observed at the same 
time, were almost equally great. The spiral band was first con- 
verted into two layers lining the two transverse walls, and these 
were connected together by a sinuous longitudinal band. At 
4 P.M. there was in one of the corners a large pear-shaped mass, 
which contracted while it was watched into an oval mass, 
and at the opposite corner a small dark-green sphere. By 
7.10 p.m. there were two spherical masses and an oval one, which 
latter by the next morning formed a much elongated dark band ; 
and instead of two there was now only a single separate sphere. 
