302 PRACTICAL COURSE IN BOTANY 
roundish particles inclosed in the chlorophyll bands? Test 
with a little iodine solution and see what they contain. 
Each filament will be seen, when sufficiently magnified, 
to consist of a number of more or less cylindrical cells joined 
tagevher in a vertical row, and thus forming the simple 
threadlike thallus which characterizes this 
class of alge. Physiologically, each cell 
is an independent individual, and often 
exists as such. Can you see the cell 
nucleus? If not, place a few filaments 
in a solution of eosin and add a drop of 
acetic acid to give the solution a pale 
rose color. After twenty to thirty min- 
utes, examine again; the nucleus will be 
Poy eee stained a deep red. If you can find an 
two filaments beginning UNbroken filament, examine both ends to 
Pe te ie Rg for- see whether there is any differentiation of 
base and apex. 
342. Conjugation. — See if you can find two filaments 
sending out lateral protuberances toward each other. 
Watch and notice that after a time these projections come 
together and unite by breaking down the cell walls divid- 
ing them, the protoplasm in each contracts, the contents of 
one pass over into the other, and the two coalesce, forming 
a new cell but little, if any, larger than the original con- 
jugating bodies. This cell germinates under favorable 
conditions and produces a new individual. This method 
of reproduction is known as conjugation. The cells thus pro- 
duced by the union of the contents of two separate cells 
may either germinate at once, and give rise to new individ- 
uals, or remain quiescent for a time, as resting spores. 
Practical Questions 
1. Are any of the green alge parasitic? How do you know? (186, 
336.) 
2. Why is their presence in water regarded as denoting unhygienic 
conditions ? 
