268 



SEEDLESS PLANTS 



a lens. Of what does it appear to consist ? Are the fila- 

 ments all alike, or are they of different lengths and thick- 

 ness ? Soak a number of them in alcohol for half an hour 

 and examine again ; where has the green matter gone ? 

 Do these algae contain chlorophyll? (Sec. 25). 



379. Spirogyra. — The filamentous algae are very numer- 

 ous, and your drop of pond scum will probably contain sev- 

 eral kinds. At least one of these, it 

 is likely, will be a Spirogyra, as this 

 is one of the commonest and most 

 widely distributed of them all. This 

 genus takes its name from the spiral 

 bands in which the chlorophyll is 

 usually disposed (Fig. 508) within 

 the cells. These bands are single in 

 some species, in others they combine 

 and intercross in various ways, form- 

 ing most beautiful patterns when 

 viewed under the microscope. Each 

 filament is seen, when sufficiently 



magnified, to consist of a number of more or less cylin- 

 drical cells joined together in a vertical row, and thus 

 forming the simple threadlike thallus that characterizes 

 this class of algae. Physiologically, each cell is an inde- 

 pendent individual, and often exists as such. 



380. Vegetative Multiplication. — Some of the algae, so 

 far as our present knowledge goes, have only the one form 

 of reproduction known as vegetative multiplication, or fis- 

 sion (splitting). A cell divides itself in two, each half 

 grows into a distinct cell, which again divides, forming 

 new cells, and so on, till millions of individuals may result 

 from a single mother cell in a few days, or in some cases, 

 in a few hours. This method of reproduction takes place 

 in some form or other in almost all plants, the propagation 

 by buds, tubers, rootstocks, runners, etc., among sperma- 

 tophytes being nothing but a mode of vegetative multi- 

 plication. 



508 509 



508, 509. — spirogyra 

 (magnified) : 50S, two fila- 

 ments beginning to conju- 

 gate ; 509, formation of 

 spores. 



