BLUE-GREEN ALGAE 103 



the peripheral cytoplasm. The phycocyanin may readily be ex- 

 tracted by killing the plant, when the plasma membrane at once 

 allows the dissolved pigment to pass out through the cell wall. 

 When plants are dried and pulverized, then soaked in water, a 

 solution of the bluish coloring matter is thus readily obtained. A 

 quicker method is to place the blue-green algae in chloroform water 

 (made by shaking up a small quantity of chloroform in water, 

 allowing it to settle, then decanting the water, which is then used 

 in the experiment), or in water containing a few drops of carbon 

 bisulphide, for a short time. Death of the plants at once ensues 

 and the dichroic phycocyanin passes out into the surrounding 

 water, leaving the filaments bright green from the remaining chlo- 

 rophyll pigment. 



Sap vacuoles occur sometimes in the cells of the Cyanophyceae, 

 particularly in the older elongated cells of such forms as Tolypo- 

 thrix and Calothrix. Another kind of vacuole, filled with gas, is 

 said by Klebahn and others to occur in certain free-floating blue- 

 green algae, such as Coelosphaerium, Anahaena, and Oscillatoria, 

 when they rise to the surface to form water-bloom. These authors 

 regard the so-called gas vacuoles as directly concerned with the 

 floating capacity of the algae which possess them; their contentions 

 have been disputed a number of times, however, and the gas 

 vacuole theory is regarded by many as untenable. 



Sexual reproduction is unknown among the blue-green algae. 

 Asexual multiphcation takes place in the simpler forms by cell 

 division and subsequent separation of the daughter cells. In the 

 higher, filamentous Hormogoneae, short one- to few-celled fila- 

 ments, known as hormogonia, are regularly set free and these frag- 

 ments form new plants. Spherical or cylindrical resting spores are 

 formed in some species by the growth in size of the vegetative cells 

 and by the thickening of the walls. 



Heterocysts are special cells developed in some forms from ordi- 

 nary vegetative cells, whose significance is not well understood. 

 Their protoplasmic contents apparently soon die and one or two 

 polar thickenings appear in the cell. Undoubtedly they are at 

 times connected with the breaking up of the filaments, but in some 

 cases they normally occur at the basal ends only of the filaments. 



