CRYPTOGAMS 299 



the club mosses, has probably given rise to at least one sec- 

 tion of the gymnosperms, while the ferns are regarded as the 

 ancestors of the true flowering plants, which make up the 

 great class of angiosperms, and represent the highest type of 

 evolution yet attained in the vegetable kingdom. 



II. THE ALG^E 



MATERIAL. Simple forms of green algae can be found on the shady 

 side of tree trunks, damp walls, old fence palings, and the outside of flower- 

 pots. Pleurococcus, one of the commonest kinds, occurs as a green, 

 powdery mat or felt in damp places, and is often accompanied by proto- 

 coccus, another good specimen for study. Spirogyra and other filamentous 

 algaB can be found in stagnant pools and ditches and in old rain barrels. 



APPLIANCES. Eosin solution, nitric acid, alcohol, iodine solution ; 

 a white china plate ; a hand lens ; a compound microscope, and slides. 



336. Variety of forms. - - This group embraces plants of 

 the greatest diversity of form and structure, from the minute 

 volvox and desmids that hover near the uncertain boundaries 

 dividing the vegetable from the animal world, to the giant 

 kelps of the ocean, which sometimes attain a length of from 

 six hundred to one thousand feet. They are usually classed 

 according to their color, as green, brown, and red algae, 

 including various subdivisions of each group. They all con- 

 tain chlorophyll, by means of which they manufacture their 

 own food, though in the red and brown divisions it is masked 

 by the presence of other pigments an adaptation to the 

 modified light that reaches them at various depths under 

 water. With few exceptions they can live only in the water, 

 and unlike any other form of plant life, attain their highest 

 development in the salty depths of the ocean. The fresh- 

 water forms are small and inconspicuous, and generally of a 

 more simple type than the seaweeds. The great majority of 

 them belong to the two classes of green and blue-green algse. 

 The former is believed to have furnished the type from 

 which the higher plants have been evolved. 



337. Study of a one-celled alga. Put a little of the green 

 algse in water on a glass slide. Hold up to the light, or 



