TYPES OF CRYPTOGAMS; THALLOPHYTES 249 



the surface of the enveloping cells which enclose the spore. What 

 is their number and form ? What is their relation to the cells form- 

 ing the crown ? Focus so as to see the larga egg-cell (oosphere or 

 obspore) which constitutes the center of the fruit. Can you determine 

 anything regarding its contents ? 



Search for young oogonia and if practicable describe and draw 

 them in several stages of development. Their structure can be seen 

 much more easily than that of the 

 antheridia. Make drawings to illus- 

 trate various details of structure. 



290. Characeae. Nitella 

 and Char a are the genera 

 composing the group CJiara- 

 cece, a group of green algse 

 differing widely from any 

 others. They show in a won- 

 derful manner simplicity of 

 cell-structure with a high 

 decree of organization. FlG - 182. Partof a Leaf of rig. isi. 



(Considerably magnified.) 



Scarcely less wonderful are a , antneridium . , o g onium. At the 

 the care and precision with - ri s ht are a y un g antheridium and 



archegonium. 



which botanists have worked 



out their life history. As a study in evolution the Characece 

 may be considered as representing the highest develop- 

 ment attained along the line of filamentous green algse, 

 which, while preserving their algal characteristics, are 

 comparable in a remarkable degree with moss- and fern- 

 plants and with seed-plants. Every cell in the plant has 

 been accounted for and is understood in regard to origin, 

 relationship, and function. With harmony of structure 

 throughout, it has organs comparable to root, stem, and 

 leaf in seed-plants, each with characteristic structure and 



