Observations on Cosmarium Margaritiferum. 35 
four hours) might be about an average time required for sub- 
division ; but the period required for the ripening of the 
moving granules, I cannot in the least calculate. I took a 
plant in apparently full maturity, and watched it for a fort- 
night ; but I could trace no change in its appearance, nor did 
the granules weary in their motion, either in sunlight or in 
shade, in daytime or at night ; for in the dead of night, when 
hours of darkness might have brought on them the " sleep of 
plants," I suddenly threw upon them a strong light, and 
found them in their usual activity of motion, while the same 
light only gradually and partially roused a " wheeler " from 
his slumbers. I have figured four monstrosities in subdi- 
vision, which I observed in the spring of 1852 (figs. 15, 16, 
17, 18). I was much inclined in 1851 to suppose, from the 
figure fig. 21, that subdivision took place at various ages of 
the plant ; I subsequently found, however, that this must 
have been a plant of C. Thwaitsii^ which I obtained in the 
spring of 1852, in a neighbouring locality, in great activity of 
division and swarming motion ; and in the same autumn I 
found sporangia of two species, which would lead me to sup- 
pose fig. 22 a full-grown form. (See figs. 25 and 28.) 
All the species of Cosmarium do not appear to have the 
habit of casting off their envelopes ; for in fig. 19, which I 
found in great abundance, both subdividing and forming 
sporangia, no loose vesicles were left from the former process, 
though in the latter the empty cases were abundant and per- 
manent. Being greatly disappointed at not being able to 
prove the use of the moving granules, I watched as minutely 
as I could the formation and subsequent development of the 
sporangia. The contents of the ball, as in the division of the 
plant, were at first light in colour, and containing few gran- 
ules ; they subsequently became darker green, and then a 
reddish-brown, as in figs. 25, 26, 27, or as in figs. 23, 24 ; 
and at the same time the coats became more numerous. 
In the month of April 1853, I was delighted to find in the 
bottle containing the sporangia of Cosmarium, fig. 24, a 
many-coated ball filled with granules in the same rapid 
motion as observed in the full-grown Cosmarium. The simi- 
larity of the movement attracted my attention ; and I also 
saw that in one part the enclosing membrane appeared thinner, 
as if giving way at that spot. On the third morning the 
membrane had broken, and the granules escaped, leaving the 
nearly-emptied case as represented at fig. 29. See also 
fig. 30. 
I will now speak of the changes visible to the naked eye, 
while preserving in bottles water in which Cosmarium margari- 
d 2 
