CHAPTER V. 



GREEN ALGJK Continued. 

 ORDER III. POND SCUMS (Conjugates). 



THE Conjugatce, while in some respects approaching the 

 Confervacece in structure, yet differ from them to such an 

 extent in some respects that their close relationship is doubt- 

 ful. They are very common and familiar plants, some of them 

 forming great floating masses upon the surface of every stag- 

 nant pond and ditch, being commonly known as " pond scum." 

 The commonest of these pond scums belong to the genus 

 Spirogyra, and one of these will illustrate the characteristics of 

 the order. When in active growth these masses are of a vivid 

 green, and owing to the presence of a gelatinous coating feel 

 slimy, slipping through the hands when one attempts to lift 

 them from, the water. Spread out in water, the masses are 

 seen to be composed of slender threads, often many centi- 

 metres in length, and showing no sign of branching. 



For microscopical examination the larger species are preferable. When 

 one of these is magnified (Fig. 18, A, (7), the unbranched filament is 

 shown to be made up of perfectly cylindrical cells, with rather delicate 

 walls. The protoplasm is confined to a thin layer lining the walls, except 

 for numerous fine filaments that radiate from the centrally placed 

 nucleus (n), which thus appears suspended in the middle of the cell. The 

 nucleus is large and distinct in the larger species, and has a noticeably 

 large and conspicuous nucleolus. The most noticeable thing about the 

 cell is the green spiral bands running around it. These are the chloro- 

 plasts, which in all the Conjugatce are of very peculiar forms. The num- 

 ber of these bands varies much in different species of Spirogyra, but is 

 commonly two or three. These chloroplasts, like those of other plants, 

 are not noticeably different in structure from the ordinary protoplasm, as 



