CRvrroGAMS 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 Avliicli are like the larger ones described above 

 and develop in a similar fasliion. 



417. Spirogyra. — Spirogyra may be found floating in 

 unattached masses at the surface of almost any sunny 

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

 Frog slime or Frog spittle. Under the microscope a Ijit 

 of the mass becomes a tangle of beaiitiful green lilaments. 



s 



2S(J. Siiirogyi-a: i/, nucleus; s, cliromatoi)Uoi'es. 



unbrancbed, and consisting of elongated cylindrical cells 

 (Fig. 28(5) placed end to end. In the cells of Spirogyra 

 tlie essential parts of the typical vegetahle cell are well 

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

 matter {protoiiJasiii), eral^edded in which are several 

 spiral bands of denser composition, the cliromatophores, or 

 color-beai-ing organs f.s), containing the chlorophyll. 

 Near the center of the cell is found the rounded nucleus 

 (/i ), from which strands of jirotoplasm run to the periplieral 

 layer. Tlie remaining space is filled with cell sap — 

 wrttei' \\ith dissolved substances. 



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

 pendence of one anotJier, eacli forming its own food 

 supplies, and exevy one capable of dividing transversely 

 to f(irm two daughter cells ; by which process the plant 

 increases rapidly under favoral>le conditions. 



1 Itcfcr liere to §§ 40:t-498 ; a full discussion of the cell should be had 

 at this jiniut. Empliasize the relative unimpoi'tance of the wall ; the 

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

 vital activity ; the r61e of the nucleus in cell division (briefly V, and the 

 occurreiH'c of many cells (represented by nuclei) in a common wall, as in 

 Vaucheria next to be described. 



