8 
POPULAR SCIENCE REVIEW. 
(13, a') 9 it appears like a green ball, becoming what has been 
called a gonidium, or spore. If this be kept on a slide in 
damp air, it will be found after a time to divide in various 
ways (see fig. 17). Some of these divisions become very small 
(fig. 17); all, however, after a time revert to the linear or 
filamentous form.* No zoospores have as yet been found in 
this alga, although they have been observed in a very closely 
allied form — namely, the Ulva, a saltwater alga. 
These confervoid algse of which we have been speaking 
exemplify the mode of growth and multiplication in these 
lower forms of vegetation. All of them, from their simple 
arrangement, can be readily observed ; but in order to observe 
them continuously, they should be placed in as natural a state 
as is possible, and that for a considerable period. When 
brought within doors, they ought, unless living in water, to be 
placed in a damp situation, covered over by a glass, with as 
much light as can be obtained ; because the reduction of light 
under cover and in a room is very great. A saucer with damp 
(not wet) sand, or a piece of sandstone will do well, covered 
over by a glass ; on the sand you can place the specimen, or, 
if under particular microscopical observation, on a glass slide, 
ready for instant use. 
But it is very important in the aquatic specimens to secure 
some water from the identical ponds from which they were 
taken. They are very sensitive to these apparently minute 
points, and the vessel in which they are kept should not be too 
deep. To have them ready for instant observation, the speci- 
men should be placed in a live-box made on purpose, having 
an apearture to admit air ; this can be obtained of most opti- 
cians. In this manner the conjugation of Spirogyra can be 
observed. Vaucheria and Prasiola can be kept best on damp 
sand. It may be mentioned that, of the plants above men- 
tioned, none require an object-glass above J-inch focus ; gene- 
rally, i-inch object-glass will suffice. 
Before closing, it may be well to call the attention of the 
reader to the circulation to be observed in the cells of 
Spirogyra ; it is best noticed near the ends of each cell, and 
near the cell-wall. Delicate streams are constantly flowing in 
varying lines, such as may be observed in the hairs of the 
Nettle, Achimenes, &c. and which has been called 66 cylosis.” 
To see this well, a high power should be used, either a J-inch 
object-glass, or, even better, a J-inch. 
* The same mode is seen in the "broad bands as shown at fig. 16. 
