224 ESSENTIALS OF BOTANY 



286. Minute Structure. — Make a drawing of one or more filaments 

 as seen with l.p. Draw the basal and the apical cell as seen with h.p. 



Under h.p. draw one of the cells near the middle of a filament 

 and note : 



(a) The large chromatophore, which almost fills the cell. 



(b) The nucleus (if it can be seen). 



(c) Pyrenoids. Test with iodine to see whether starch is present. 



287. Eeproduction. 



I. Asexual 



"With h.p. look for cells in any of the filaments in which the proto- 

 plasmic body of the cell has changed into a pear-shaped cell (zoospore) 

 furnished at the smaller end with a fringe of cilia, or bristle-shaped 

 appendages. Look also for the pear-shaped zoospores swimming 

 freely about by means of their cilia. Study their movements, then 

 run in iodine under one edge of the cover-glass, to kill the cells, and 

 note the form and structure of the zoospore. Draw. If any germi- 

 nating zoospores can be found, draw them. 



II. Sexual 



With h.p. look for filaments which have large swollen cells at 

 intervals along their length. Such a cell is called an oogonium, and 

 contains one female gamete, or egg. Note : 



(o) The general form of the oogonium. Draw. 



(6) The pore or opening to allow of fertilization. 



(c) The egg-cell which nearly fills the oogonium. 



Look for antlieridia, groups of rather flat, tabular cells occurring 

 near oogonia. These produce ciliated sperms, which enter the egg- 

 cells and fertilize them. Draw a group of the disk-shaped cells. 



Look for fertilized egg-cells, which may be distinguished by their 

 heavy cell-walls. This fertilized cell is an oospore. In the oospores 

 seen note : 



(a) The dense cell-contents, due to the accumulation of food 

 material. Test with iodine solution for starch. 



(h) In the older oospores the division of the contents into ciliated 

 zoospores, each of which may grow into a new filament of (Edogonium. 

 Draw oospores at various stages. 



