Cameron: Morphology of Blue-Green Algae 413 



groups. It is recognized that the major taxa of algae may show Httle afi&nity 

 with each other (Papenfuss, 1955), but they are still grouped on the basis of 

 an "algal-type" of organization, the parallelism cited in the evolution of plant- 

 body types, the morphology and physiology of the individual cells (Smith, 

 1950), photosynthates, and especially in regard to the principal protoplasmic 

 pigments (Dougherty and Allen, 1960). Blue-green algae contain the phyco- 

 bilins C-phycoerythrin and C-phycocyanin not found in other algae or bacteria 

 although phycobilins are characteristic for red algae and have also been found 

 in other groups, e.g., green algae and cryptomonads (Eocha, 1960). Chlo- 

 rophyll a, and /3-carotene are shared in common with other algal groups, but 

 certain carotenes and xanthophylls are unique to blue-green algae (Goodwin, 

 1960). By means of a fluorescence microscope, the pigments are found to show 

 an orangish red, red, or reddish brown fluorescence in a darkened background. 

 Photosynthates include polysaccharides and glycoproteins, and cell contents 

 may become brown when treated with I-KI solution. 



In some species cells form reproductive spores which are denoted from 

 other cells by their larger size, thick walls, and more resistant nature. Color- 

 less cells, or heterocysts, are also formed in some species. Their function and 

 necessity are doubtful although they have been observed to germinate (Geit- 

 ler, 1921), and they have been noted to anchor the trichome to the firm sheath 

 (Bornet and Flahault, 1886). Endospores, undifferentiated reproductive cells, 

 are formed by 1 family, the Chamaesiphonaceae, but for filamentous taxa, the 

 random death of individual cells permits segments of trichomes, or hormogonia, 

 to propagate the species when moisture is available. Cell division is by fission, 

 i.e., constriction into two parts, or by centripetal progression of a dividing 

 membrane through the protoplast. Reproduction is frequently by fragmenta- 

 tion. Sexual reproduction, although recently reported for a strain of Nostoc 

 muscorum (Lazaroff and Vishniac, 1961), is not considered characteristic for 

 the group. 



Cytologically, the cells are found to have the aforementioned pigments, pro- 

 tein granules, pseudovacuoles of a gaseous nature, and occasionally vacuoles, 

 within a containing membrane. Pseudovacuoles are characteristic of plank- 

 tonic "water-blooms"; they appear black in transmitted light, red in reflected 

 fight, and are dissolved when treated with detergent. Vacuoles occur in old 

 or degenerated cells, particularly as the environment becomes anaerobic. The 

 protoplast is said to be clearly divisible into two parts (Desikachary, 1959) : the 

 pigmented, peripheral chromoplasm and the central colorless centroplasm. 

 It also may be recognized, however, that such a strict differentiation is super- 

 ficial. Feulgen positive granules are found particularly in the centroplasm 

 (Cassel and Hutchinson, 1954). Pigments are reported to be in grana-like 

 lamellae of the chromoplasm according to electron microscope studies (Niklo- 

 witz and Drews, 1956). Few studies on nucleoproteins of blue-green algae 

 have been undertaken although it has been reported that these are similar to 

 those recorded for tissues of other organisms (Biswas, 1961). 



Classification 



The Myxophyceae have been classified in one or more orders. The classi- 

 fication followed here considers the blue-green algae to be in a single order. 



