OSC ILL ARIA TEN U IS. . 31 



ANNOTATIONS. 



If the structure of Oscillaria be carefully compared 

 with that of Protococcus more points of resemblance 

 will be found than appear at first sight. New cells are 

 formed by the process of division, as in Protococcus, 

 but the partition walls are always parallel and in one 

 direction, which disposes the cell families in filaments. 

 The individual cells have thin walls, the office of pro- 

 tection being relegated to the sheath. The sheath, 

 which is formed from the outside walls of the cells by 

 a modification of the outer portion, is a structure that is 

 mostly confined to certain groups of the lower plants, 

 although it has some analogies with the cuticle of the 

 higher plants. The protoplasm is homogeneous, and 

 not differentiated into chlorophyll bodies and nucleus 

 as in Protococcus ; chlorophyll is, however, present, 

 evenly distributed through the protoplasm, but no 

 nucleus has yet been discovered. The study of the pro- 

 toplasm and chlorophyll is much obscured by the pres- 

 ence of the peculiar coloring matter, phycocyanine, 

 characteristic of the Cyanophycece to which Oscillaria 

 belongs. It is this that gives the deep blue-green color 

 to the plants, enabling one to distinguish them at sight. 

 It is insoluble in alcohol, but soluble in water when the 

 plants are dead, while chlorophyll is soluble in alcohol, 

 but not in water; hence, digesting the dead plants with 

 water removes the phycocyanine, and digesting with 

 alcohol removes the chlorophyll. 2 This blue color is 

 often seen on the sides of vessels in which Oscillaria 

 has remained so long as to die, and also staining the 

 8 Cf. Sachs, Text-book of Botany, 2nd Eng. ed., p. 246, 766. 



