Algae, Fungi, and Lichens. 271 



look upon it as one of the simplest forms which have 

 essayed to appropriate the energy of the sunlight for the 

 manufacture of their food; and it, or some form not dis- 

 tantly related to it, probably represents the very primitive 

 organism from which the higher plants have been evolved. 



Pleurococcus multiplies by cell division, one becoming 

 two, two four, etc., as in the case of the bacteria. When 

 examined under the microscope, the individuals are usually 

 found adhering in groups in a manner which suggests that 

 they are on the border land of unicellular and multicellular 

 forms. 



164. Spirogyra. Among the forms of filamentous Algae 

 taken from fresh water, Spirogyra and Oedogonium are 

 quite likely to occur. The method of reproduction of 

 Oedogonium has already been described on page 163, and 

 Spirogyra (Fig. 137) will now be used as a type of fila- 

 mentous Algae. Each individual consists of similar cells 

 joined end to end. The cytoplasm lines the cell wall, leav- 

 ing a large vacuole filled with cell sap. Embedded in the 

 cytoplasm are one or more elongated and spirally coiled 

 chloroplasts. A rather large nucleus is suspended at the 

 center of the cell by arms of cytoplasm which extend to 

 certain bodies, known as pyrenoids, embedded in the 

 chloroplasts. When a filament is mounted in a drop of 

 chloral hydrate-iodine, starch is found to be clustered about 

 the pyrenoids, and at no other places in the chloroplasts. 

 We may conclude from this that while the chloroplast is 

 undoubtedly manufacturing food throughout its whole 

 body, the pyrenoids are the centers of accumulation of 

 reserve materials in the form of starch (Fig. 137). When 

 actively growing filaments are kept in the dark for a few 

 days, the starch disappears. The chloroplasts utilize the 

 sunlight in the same manner as do the chloroplasts in the 



