72 T1IK H'/TJtY OF L/17A7,' ('KLL8. 



its passage to the end of the tube, from which it goes to perform 

 the office of fertilization when in contact with the oosphere of the 

 embryo sac. If the pollen grains of Malvaceae are used, observe _ 

 the relation of the pollen tubes to ike processes or prottiberences on 

 the grains. 



The culture slide can be kept for several days, and the devel- 

 opment of the pollen tubes observed at intervals. For figures of 

 developing pollen tubes see: Bot. Gazette, 1886; Goebel, p. 365; 

 Strasburger, pp. 304, 320; Goodale, p. 429. 



CASE II. 



Cells in Colonies, Joined Temporarily. 



Showing CELLS in COLONIES, also PROTOPLASM, CHLOROPHYLL in 

 SPIRAL BANDS, and PROGRESSIVE CELL DIVISION. 



Illustration : Spirogyra. This genus of filamentous un- 

 branched aquatic plants belong to the Conjugatae, a group of 

 Thallophytes (See Sachs' Text Book of Botany, p. 25; Bessey's 

 Botany, p. 232.) Spirogyras, when in the vegetative state, are 

 bright green, and have a silky luster when taken from the water. 

 They vary much in diameter of the filament in different species, but 

 are seldom over .15 m. m. They frequently occur in fresh pools or 

 slow flowing streams,* and may be found in winter in pools that do 

 not freeze. Most species pass into a reproductive stage in early 

 summer. But few species are known to conjugate in the winter. 



PREPARATION FIRST: Place a few of the filaments on a slide 

 in water. 



OBSERVE : 1. Cells placed end to end. 



2. The septa, or transverse partitions, plain in some fila- 

 ments ; possibly in others a box-like area will be observed at the 

 septum. 



3. The spiral band or bands, of bright green color, part 

 chlorophyll pigment and part protoplasm. Ascertain if possible 

 the number of bands. To do this, count the number that cross a 

 thread between the two points where it touches the opposite sides 

 of the ceH, and this number plus one, will be the number of bauds 

 in the cell. 



