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. 
Il. THE ALGH 
Materrau. — Simple forms of green alge 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 
alge can be found in stagnant pools and ditches and in old rain barrels. 
Appiiances. — 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 alge, 
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 alge. 
The former is believed to have furnished the type from 
which the nigher plants. have been evolved. 
337. Study of a one-celled alga. — Put a little of the green 
alge in water on a glass slide. Hold up to the light, or 
