SOME TYPES OF FLOWERLESS PLANTS. yA | 
268. Motile Form of Protococcus. — Occasionally the Protococcus 
cell may be found in an actively swimming condition, known as its 
motile form. The larger motile cells are either naked or are covered 
with a cell wall, which the colored cell-contents does not entirely fill. 
The former condition is represented by Fig. 191, I, the latter by IL. 
These large motile cells may multiply by a process known as fission into 
twos or fours, or the whole cell-contents may break up into as many as 
32 portions, each of which then sets out 
in an independent existence as a freely 
swimming spore (zodspore), Fig. 191, III. 
The change from the still to the motile 
form appears to be favored by heat, sun- 
light, and abundance of air-supply (as 
by shallowness of the water in which 
the plants are growing); the reverse 
change is brought about by conditions 
just the opposite of those above men- 
tioned. 
269. Nutrition of Protococcus.— Fe. 191.—Motile Cells of Proto- 
Protococcus can flourish only in the coceus. (Greatly magnified.) 
sunlight, but with a sufficient supply of I, protoplasm without cell wall; 
light it can absorb and fix carbonic acid =‘; protoplasm enclosed ina loose 
dame : cell wall; III, a much smaller 
gas (giving off at the same time bubbles s itite cell eotsnorey 
of oxygen) and can assimilate mineral 
substances. It is a capital example of an individual cell capable of 
independent existence. 
Ill 
THE STUDY OF SPIROGYRA.! 
270. Occurrence. — Spirogyra, one of the plants commonly known 
as pondscum, or ‘‘ frog-spit,’? occurs widely distributed throughout the 
country in ponds, springs, and clear streams. It is of a green or yellowish- 
green color, and in sunny weather usually floats on or near the surface 
of the water buoyed up by the numerous oxygen bubbles which it sets 
1If Spirogyra is not easily found, the teacher may advantageously use Zyqnema 
or Mesocarpus. He should become familiar with the appearance of some of the 
fresh-water algze by microscopical studies of them and by reference to the figures in 
such works as Wood’s Fresh-Water Alge. There are many excellent small cuts of 
common forms in Campbell’s ELlements of Structural and Systematic Botany, pub- 
lished by Ginn & Co. The teacher may consult this latter book to great advantage 
throughout his studies on eryptogamous plants. 
