STUDIES OF SPORE-PLANTS 



249 



Sphaerella is in some books called Haematococcus (mean- 

 ing blood-berry). This is only one of many examples of 

 plants which have two names. The explanation is that it is 

 one of the rules of the botanical societies that the name 

 first given by a scientific man who accurately describes a new- 

 found species should be the accepted one. In the case of the 

 plant under discussion, there is still some doubt regarding 

 the first description ; and hence there must 

 be further investigations before it can be 

 decided that one of the names is to be kept 

 in the scientific books of the future and the 

 other allowed to become obsolete. There 

 are many other such undecided problems 

 concerning the naming of other plants, and 

 also of animals. 



239. Spirogyra. In many ponds and 

 streams there are floating green masses of 

 delicate thread-like plants popularly known 

 as pond-scum. These threads are com- 

 posed of a row of elongated cylindrical cells 

 (Fig. 76), with their chlorophyll arranged 

 in one or more spiral bands. A large nu- 

 cleus may be seen near the center of each 

 cell. The cells grow and divide so as to 

 form long filaments composed of chains of 

 cells. Each cell is an individual plant, because it is capable 

 of carrying on all the life-processes of a green plant. 



Under certain conditions a tube may grow so as to join 

 two adjacent cells of the same or of separate filaments, and 

 through this tube the protoplasm of one of the two cells passes 

 into .the other and the united substance forms a spore 

 (zygospore). This later germinates and forms a cell which 

 by repeated growth and division forms a filament or chain 

 of cells. This process leading to spore-forming is known 

 as conjugation. A similar process occurs in the black mold 



FIG. 76. A cell from 

 a filament of Spi- 

 rogyra. A;, nucleus 

 in center; two 

 spiral bands con- 

 taining chlorophyll 

 (ch). 



