CRYPTOGAMS 



173 



Ulothrix the zygospore forms a wall about itself, rests for 

 a time, then makes some growth by elongating and 

 enlarging, and finally its contents break up into several 

 zoospores which are like the larger ones described above 

 and develop in a similar fashion. 



417. Spirogyra. — Spirogyra may be found floating in 

 unattached masses at the surface of almost any sunny 

 pool or spring in warm weather. It is often known as 

 Frog slime or Frog spittle. Under the microscope a bit 

 of the mass becomes a tangle of beautiful green filaments, 



286. Spirogyra: ?^, nucleus; s, chromatophores. 



unbranched, and consisting of elongated cylindrical cells 

 (Fig. 286) placed end to end. In the cells of Spirogyra 

 the essential parts of the typical vegetable cell are well 

 seen.i The wall is lined with a thin layer of living 

 matter (jcrofo/?/as?7i), embedded in whieli are several 

 spiral bands of denser composition, tlie chromatophores^ or 

 color-bearing organs (s), containing the chlorophyll. 

 Near the center of the cell is found the rounded nucleus 

 (?i), from which strands of protoplasm run to the peripheral 

 layer. The remaining space is filled with cell sap — 

 water with dissolved substances. 



418. The cells of the filament live in apparent inde- 

 pendence of one another, each forming its own food 

 vsupplies, and every one capable of dividing transversely 

 to form two daughter cells ; by which process the plant 

 increases rapidly under favorable conditions. 



1 Refer here to §§ 494-498 ; a full discussion of the cell should be had 

 at this point. Emphasize tlie relative unimportance of the wall ; the 

 idea of the living unit having the nucleus as the center and conservator of 

 vital activity ; the role of the nucleus in cell division (briefly); and the 

 occurrence of many cells (represented by nuclei) in a common wall, as in 

 Vaucheria next to be described. 



