1 8 OUTLINES OF PLANT LIFE. 



naay be readily recognized, during their vegetative period, 

 by their unbranched filaments, bright green color, and slippery 

 " feel" between the fingers.* 



Under the microscope, they are at once distinguished from other filamen- 

 tous algse by the shape of their chloroplasts. In Spirogyra these form one 

 or more flattish, spirally wound ribbons, notched on the edges, and em- 

 bedded in the protoplasm near the cell- wall {ch, fig. 1 6). In Zygnema 

 there are generally two irregularly star-shaped chloroplasts (fig. 17) ; while 

 in Mougeotia a single flat , plate-like chloroplast, nearly as wide as the cell, 

 traverses its center (fig. 1 8). See also fig. 19. 



Embedded in the chloroplasts of these and other algse are usually seen 

 one or more angular, colorless bodies, often surrounded by a jacket of 

 starch. These are stores of reserve food, known as pyrenoids {f, figs. 

 16, 18). 



In these plants there is little or no. difference between the 

 parts of the filaments. If broken into two, each part may 

 continue growing with no damage to any part except the cells 

 which were ruptured in severing the plant. 



EXERCISE IV. 



Spirogyra. — If fresh material is available examine a few filaments in a 

 white dish for color. If preserved material is used, stain red by immers- 

 ing for a few minutes in eosin (cheap red ink will answer). 



Examine with a lens. Observe 



1. Length ; whether broken or whole ; whether with or without 

 brauches. 



2. The delicate partitions, like white lines, crossing the green (or red) 

 filaments, dividing the protoplasm of one cell from another. Can the 

 form of the chloroplasts be seen ? (Cf. fig. 16. ) This can be readily seen 

 only in the larger species. (^ 23.) 



3. Demonstration. Mount a few fresh filaments in water. Show under 

 moderate power the form of the chloroplasts ; the reserve food nodules ; 

 the nucleus. (Fig. 16.) 



* This slipperiness is due to the gelatinous outer part of the cell-wall 

 (fig. 26), which is only visible after special treatment or on examining 

 the filaments in a thin mechanical solution of Chinese ink. 



