THE ALGA 221 
Osecillatoria grows in the same kind of region as Wostoe, but 
is more abundant. It appears us floating mats or as slimy coat- 
ings upon objects in the water. Frequently sticks and stones 
on the bottom are covered with a beautiful velvety layer con- 
sisting of multitudes of these simple plants. The individual 
plants are thread-like (fig. 173) and often have a swinging, glid- 
ing, or oscillating movement, from which the name of the plant 
is derived. In stagnant or foul 
water Oscillatoria plants grow bse 
vigorously, being able to thrive Cs 
throughout a wide range of tem- poe 
perature. The cells of the plant eae 
divide, thus lengthening the esl 
l 
plant. Later the threads break 
into two or more new threads, [ age | 
each of which continues to grow | Seve 
ie 
as an independent plant. The 
cells of one plant are inclosed 
in jelly-like sheaths, but there is 
no jelly mass which holds many me iy pacts 
plants wage ther, ceghe. A, tips of several plants; B, part of 
It is evident that blue-green one plant, enlarged to show cellular 
algze live and reproduce them- structure. Both magnified, B much 
: . more than 14 
selves in very simple ways. 
205. The green alge: Pleurococcus. This green alga is very 
widely distributed and is often called green slime, because of 
the appearance it presents when growing upon partially shaded 
tree trunks, fences, rocks, and old buildings. It is not usually 
recognized as being a plant. When there is abundant moisture 
in the air, the coating of plants presents the appearance of a 
coating of green paint upon the surface which supports them. 
When examined under suitable magnification, the green slime 
is seen to be composed of many thousands of single-celled 
plants. A careful measurement of a number of plants showed 
their average diameter to be about 355 inch (.014 mm.). In 
other words, it would require approximately 500 of these 
Y By 
