THALLOPHYTES 



and characteristically shaped chloroplasts. There is no reproduction 

 by motile spores, and no motile cells of any kind are formed. Sexual 

 reproduction is effected by the conjugation of protoplasts brought 

 together usually through conjugating tubes, and while in a general way 

 only isogamy is attained, there is evident in some forms an incipient 

 heterogamy shown by the different behavior of the pairing protoplasts. 

 The group as a whole seems to stand stiffly apart from all those previ- 

 ously considered, and must be regarded as very highly specialized. 



(f) Chorales 



General character. The stoneworts, as these forms are called, con- 

 stitute a very isolated group among thallophytes, which seems to hold 

 no definite relation to any other 

 group. If they are algae, they 

 must be included among the 

 green algae ; but they are con- 

 sidered by many to be quite 

 separate from algae ; and some 

 would even remove them from 

 thallophytes. Until something 

 more is known of their relation- 

 ships, however, it is convenient 

 to consider them in connection 

 with the green algae. They are 

 found in fresh and brackish 

 waters, attached to the bottom 

 and covering large areas with a 

 dense mass of vegetation. Some 

 of the bodies are incrusted by 

 such an abundant deposit of 

 calcium carbonate that it makes 

 them rough and brittle, and sug- 

 gested the name stoneworts. 

 The common genera are Cham 



FIG. 113. Chara: showing general habit 

 of body. 



and Nitella, and the general 

 structure is very uniform. 



Vegetative body. The vegetative body consists of a cylindric stem or 

 main axis which branches profusely (fig. 113). All of the axes are dif- 

 ferentiated into short nodes and long internodes, and from the nodes the 



