TYPES OF CRYPTOGAMS; THALLOPHYTES 247 
zoospores are formed in this way, having their entire surface clothed 
with cilia. They are the largest motile cells known. In other spe- 
cies a portion of the filament is separated and cut off by a cell-wall. 
Such spores soon germinate and may be found in various stages of 
growth. They often serve for propagation through several genera- 
tions before spores are produced by fertilization. 
With a power of about 200 diameters sketch a portion of a fila- 
ment to show the form and location of chlorophyll. Sketch the 
fruiting organs in detail, if any can be found. 
Antheridia and oégonia are formed near together on the same 
filament. The antheridium is a cell forming the terminal portion 
of a short branch, which is rather slender, straight or curved. Its 
contents form numerous minute antherozoids, each with two cilia. 
The cilia can be seen only with great difficulty, if at all, but their 
presence is indicated by their active movements. ; 
The odgonium is a short, somewhat spheroidal branch separated 
by a cross-partition at the base. The cell-wall becomes ruptured at 
the tip, allowing the entrance of the antherozoids by which it is 
fertilized. After fertilization a cell-wall is formed about the odsphere, 
and it matures as an odspore and enters upon a period of rest. 
THE STUDY OF NITELLA 
285. Occurrence. — Nitelia is a green plant growing attached to 
the bottom of ponds and streams, usually in shallow water. It is 
not common everywhere but is widely distributed. Chara is similar 
and may be used as a substitute but is more complicated. 
286. General Aspect.— With the naked eye and a magnify- 
ing glass note the general aspect of JNitella, the length of the stem- 
like portions, from the root-like parts to the tip, the length of some 
of the joints (internodes), the arrangement of leaf-like and branch- 
like portions. 
287. Protoplasm. — Examine the cells of stems or leaves under a 
low power. Select a vigorous cell of moderate size and examine 
1 Goebel states that the formation of the fruiting organs begins in the even- 
ing, is completed the next morning, and that fertilization takes place during 
the day between ten and four o’clock, 
