302 



PRACTICAL COURSE IN BOTANY 



430 



431 



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 

 together in a vertical row, and thus forming the simple 

 threadlike thallus which characterizes this 

 class of algse. 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 

 Figs. 430, 431.— <Spi- stained a deep red. If you can find an 



rogyra (magnified) : 430, • i xi j - 



two filaments beginning uubrokeu filament, examine both ends to 

 to conjugate; 431, for- gge whether there is any differentiation of 



mation of spores. '' 



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 algtc parasitic? How do you know? (186, 

 336.) 



2. Why is their pre.sence in water regarded as denoting unhygienic 

 conditions ? 



