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 IJirough 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.i 



Antheridia and oogonia 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 aU, but their 

 presence is indicated by their active movements. 



The oogonium 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 oosphere, 

 and it matures as an oospore and enters upon a period of rest. 



THE STUDY OF NITELLA 



285. Occurrence. — Nitella is a green plant growing attached to 

 the bottom of ponds and streams, usually in shallow water. It is 

 not common everyTvhere 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 Nitella, 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. 



