NOSTOCHINEiE. 
Ill 
those in the neighbourhood of the heterocyst. Finally, at maturity, the threads break 
up, and the enlarged brown cells are found to contain spores which germinate and 
continue the species. They have been stated to change into zoospores, but this requires 
confirmation. M. Thuret , in a communication recently made to the Natural History 
Society of Cherbourg (Aug. 1857, vol. 5 ) has described and figured the germination 
of the spores of Anabaina licheniformis , and A. major. In these species the sporan- 
gium is oblong, and contains at maturity a deep brown solitary spore. M. Thuret 
having obtained some specimens with ripe fruit, set them aside in a convenient glass 
vessel, and observed them from day to day. The filaments soon broke up, the hetero- 
cysts and sporangia floating apart in the water. Many of the la,tter perished, melting 
away, and disappearing altogether. Some remained sound, and these were carefully 
supplied with water, until germination commenced. The spore, in germinating, at 
first lengthens, pushing against one end of the sporangium, which it finally pierces 
lifting off the tip of the periderm like a lid, and thus its extremity issues, as the radicle 
from an monocotyledonous seed, capped with the lid of the sporangium. At this period 
new cells begin to be formed, by the repeated sub-division of the spore, which continues 
to lengthen till it is transformed into a moniliform filament or string of cells, like that 
from which it was derived. At first the divisions between the cells are but little 
distinct, but they become more and more strongly defined as growth proceeds. The 
filament lengthens at both extremities, but more rapidly at that which projects into the 
water ; the young articulations are of smaller size than the rest, and thus the filament 
tapers towards each end. But this character gradually disappears, and the cells acquire 
a uniform dimension, proper to the species. M. Thuret s first experiments were made 
with freshly gathered sporangia : but he afterwards succeeded in causing to germinate 
specimens which had been dried and preserved for several months in the herbarium* 
They began to germinate in about a fortnight. Others (of Anabaina licheniformis) 
which had been kept for nine years in a dried state, germinated in an equal space of time, 
and the experiment was repeated several times with like success. Several other fresh- 
water Algae have been observed to possess the same property of revivification, and it 
seems a necessary endowment to enable them to continue the existence of their species 
through the alternate drying and moistening to which they are subjected in nature. 
To M. Thuret we are also indebted for observations on the ordinary propagation by 
gemmation of the Nostocs , and for an account of the way in which the compound frond 
is developed. In the autumnal months, when this process goes forward, the old Nostoc 
may be said to diliquesce, the gelatine becoming loose and exuding, and the filaments 
contained in it breaking up into small fragments. If these be collected and placed in 
a glass of water, they may be observed to have a slow, progressive movement, like that, 
of the Oscillator ice, which enables them to change their place ; and at length they 
generally fix themselves on that side of the glass next the light. By continuing the 
observations for some days, the broken threads are seen to become immoveable, and 
then to be invested with a transparent pellicle. At the same time the green cells 
increase in size, expanding laterally, till the thread attains nearly twice its ordinary 
diameter. A cell division, in vertical order, then takes place throughout its component 
cells, and thus the filament splits into two parallel filaments, which are then contained 
