SOME COMMON OBJECTS 55 



a single line of cells growing end to end. Zygnema 

 is one form and Spirogyra another. The latter is 

 very common ; in slow-running streams it is often 

 seen hanging from weeds in long streamers, while in 

 stagnant waters it grows independently in scum- 

 like masses. It is also common in roadside drinking- 

 troughs. The threads are exceedingly fine, and 

 should be examined in water on a glass slip with 

 thin cover, with an objective of not less than 

 ^-inch power. Two or three pieces of a filament are 

 sufficient. Each cell is characterized by the spiral 

 chloroplasts, which are bright green in colour. 

 Treat the object with iodine solution ; the cell 

 contents wiU be stained, and the nucleus and 

 nucleolus will appear, while the protoplasm will 

 assume a yellow colour. 



By carefully examining selections from a mass of 

 Spirogyra, the worker may chance to find two fila- 

 ments in conjugation. Two threads come together, 

 and some of their cells put out tiny processes by 

 which the threads become united. Such filaments 

 lose their usual appearance ; the chloroplasts lose 

 their spiral form ; the cell walls are being absorbed, 

 and a way is being made for the contents of the cells 

 of one thread to pass into the cells of the other. In 

 due course the blended cell contents will form spores, 

 f rom'Vhich'new plants will develop . 



The cells in the leaves of the Canadian water- 

 weed (Elodea) exhibit remarkable movements of 

 their protoplasm, a movement described as circula- 

 tion. The same phenomenon is displayed in a more 

 or less clear manner by the Frogbit (Hydrocharis) 

 and Vallisneria spiralis. To observe this movement 



