114 



A TEXT-BOOK OF BOTANY 



conspicuous objects. The band is not flat, and to deter- 

 mine its form is an excellent exercise for a student learn- 

 ing to reconstruct objects under the microscope. Embed- 

 ded in the chlorophyll band nodule-like bodies (pyrenoids) 

 are seen, around which a granular zone of starch grains is 

 often visible. In favorable material, notably cells with a 

 single band, the nucleus may be seen, surrounded by a zone 

 of cytoplasm that is connected by radiating strands with 

 the cytoplasm against the wall (Fig. 103). 



Spirogyra is peculiar in producing no swimming spores, 

 or asexual spores of any kind. Its method of sexual re- 



FIG. 105. Spirogyra, showing some common exceptions: A, two connected cells 

 that have formed oospores without fusion, and a second cell that has attempted 

 to connect with one of them; B, cells of three filaments, the cells of the cen- 

 tral one having connected with both the others. 



production also is peculiar. | i Cells > of two adjacent fila^ 

 ments put out protuberances toward one another; and where 

 they come in contact an opening is formed, the result being 

 that there is a continuous passageway connecting a cell of 

 one filament with a cell of the other (Figs. 104 and 105). 

 When many of the cells of two parallel filaments become 

 thus united, the appearance is that of a ladder, with the 

 filaments as the side pieces and the connecting tubes as .the 



