TYPES OF CRYPTOGAMS; THALLOPHYTES 245 



"Note that in reproduction the cell-contents in many individuals 

 has divided into two parts which become separated from each other 

 by a cellulose partition. Each of these again divides, and the proc- 

 ess continues until thirty-two or more cells may be found in one 

 mass or they may fall apart at an earlier stage. 



279. Nutrition of Pleurococcus. Pleurococcus can nourish only 

 with an abundance of light and moisture. In daylight it can absorb 

 carbon dioxide and fix carbon (giving off the oxygen at the same 

 time as bubbles of oxygen) and can assimilate mineral substances. 

 It is a capital example of an individual cell capable of independent 

 existence. 



280. Motile Forms. No motile form is known in Pleurococcus. 

 Hcematoccus, often known as Protococcus (Fig. 179), is a better object 

 for study than Pleurococcus. It may sometimes be found in water 

 of stagnant pools, particularly those which contain the drainage of 

 barnyards or manure-heaps, in mud at the bottom of eaves-troughs, 

 in barrels containing rain-water, or in water standing in cavities in 

 logs or stumps. Its presence is indicated by a greenish or some- 

 times by a reddish color. It is sometimes found in an actively 

 swimming condition, in which case each cell is called a zoospore. 



THE STUDY OF VAlJCHERIA 



281. Occurrence. Species of Vaucheria are found in ponds, 

 streams, and pools, immersed or floating like Spirogyra and at all 

 seasons may be sought in greenhouses, where they grow on the moist 

 earth of beds and pots, forming a green felt. 



282. Examination with the Magnifying Glass. The magnifying 

 glass will show the growth of Vaucheria to consist of numerous 

 green filaments similar to those of Spirogyra. Select a srnall portion 

 and spread out the filaments carefully in a drop of water on a slide. 

 Does the -glass reveal any indications of cross-partitions, of branch- 

 ing, or of fruiting organs as short lateral branches ? Does it show 

 the form or arrangement of the green coloring matter? 



283. Examination with the Microscope. Prepare as directed 

 for the magnifying glass and place a cover-glass over the prepara- 

 tion, with sufficient water. With the lowest power observe the 



