XL 

 SPIROGYRA. 



In ponds and tanks, the water of which is tolerably pure, 

 we constantly find in summer floating masses, of a light 

 green colour, which feel slippery when handled. A very 

 superficial examination is sufiicicnt to show that these 

 masses consist of a vast number of very long and fine green 

 threads. The organisms in question may belong to various 

 genera of a group of plants called the Coifervoid Algae: 

 one of the genera, representatives of which are most com- 

 monly found, is Spirogyra. 



On microscopical examination we find that each thread 

 of Spirogyra consists of a single, unbranched, row of 

 cylindrical cells, of very variable length, but of constant 

 diameter throughout the filament. There is no distinction 

 of apex and base ; both ends of the filament are quite 

 alike, and neither is attached to any substratum. We have 

 to do here with a plant which is morphologically multi- 

 cellular, for each thread consists of many cells. All these 

 cells, however, are uniform in structure, and each performs 

 for itself, so far as can be ascertained, all the functions of 

 the plant. Hence Spirogyra may be spoken of as phy- 

 siologically a unicellular plant. In each of the cells there 

 are one or more (sometimes as many as lo) bright green 

 spiral bands, and by these the genus may at once be 

 recognized. Their number varies according to the species, 

 which are very numerous, and in many cases hard to 



