80 BOTANY 



Gunnera have a Nostoc associated with them, and many of the 

 Lichens have species of Schizophyceae forming their "gonidia." 

 This habit of associating themselves with other living organisms, as 

 well as their frequent preference for water containing organic matter, 

 indicates a certain dependence on organic food which is not found in 

 the higher green plants. 



Structure of Schizophyceae 



The simplest forms among the Schizophyceae are unicellular, but 

 more commonly the cells are united into filaments of definite form. 

 The cells are either approximately globular, e.g., Nostoc, Cliroococcus, 

 Anabaena; or they are cylindrical, e.g. Oscillatoria, Scytonema. 

 There has been much controversy over the structure of the cell, and 

 there is still more or less difference of opinion concerning the nature 

 of some of the structures. Some Schizophyceae live isolated, but 

 usually they occur in large masses. 



The Cell- wall. The cell-wall may be thin, but is more commonly thick and 

 gelatinous, seldom showing the reaction of pure cellulose, but usually resembling 

 more the cutinized membranes of the higher plants. It is often colored yellow, 

 or sometimes red or purple. In many forms, e.g. Rivularia, Nostoc, etc., the 

 plants are imbedded in large gelatinous masses, derived in part from a change in 

 the cell-wall, but probably, for the most part, a direct secretion of the cells. 

 Like the gelatinous colonies of Bacteria, which they much resemble, these are of 

 characteristic form and color in each species. 



The Protoplast. In the larger Schizophycese the protoplast usually shows a 

 more or less evident differentiation into a peripheral layer, to which the pigment 

 is confined, and a central colorless part, the central-body, which is often irregula. 

 in outline, and whose nature is still not certain. The central-body may repre- 

 sent a rudimentary nucleus, but this has been disputed. The chlorophyll, which 

 is associated with a blue pigment (phycocyanin), is confined to the peripheral 

 cytoplasm, but whether the whole cytoplasm is uniformly stained, or whether 

 there is a special chromatophore, is not agreed upon. A definite chromatophore 

 can certainly be detected in the young heterocysts of Anabaena (see Fig. 56, D), 

 and it seems likely that a chromatophore may be assigned to all the higher forms, 

 at least. Granules may generally be seen in the protoplast, and these it is claimed 

 are of two kinds, the so-called Cyanophycin-granules, which are confined to the 

 peripheral protoplasm, and are reserve-food granules, and the Central granules, 

 which belong to the central-body, and are probably allied to the chromatin-gran- 

 ules of a true nucleus. 



Pigments. The Schizophyceae contain, in addition to the chloro 

 phyll, a second pigment, usually a blue one (Phycocyanin), but 

 sometimes a violet or orange-yellow modification of this pigment. 

 The phycocyanin is readily soluble in water, and in drying speci- 

 mens for the herbarium, it often makes a bright blue stain on the 

 paper. The extract obtained by placing dried and powdered speci- 

 mens in water appears pure blue if seen by transmitted light, but 

 by reflected light it shows a marked purplish red fluorescence. The 



