308 



BOTANY 



soil or floating in water in the form of gelatinous masses, in which are embedded the 

 unbranched cell filaments like rows of beads. Heterocysts poorly supplied with 

 cell contents occur at irregular intervals (Fig. 227, h) in these chains of cells, while 

 from the vegetative cells, richer in contents, spores 

 (sp) are produced. On germination these spores 

 give rise to a new filament composed of similarly 

 united cells (Fig. 227, B, C). 



In certain Nostocaceae the cell filaments are 

 characterised by false branching. This pseudo- 

 branching occurs when a cell of a filament becomes 

 bent outwards and is pushed upwards by the con- 

 tinued division of the lower cells, so that the 

 upper portion assumes the appearance of a lateral 

 branch. 



Many Cyanophyceae take part with the 

 Fungi in the formation of Lichens. Some 

 species also are endophytic and inhabit 

 cavities in other plants. Thus, species of 

 Fio. 227.— Nostoc Lincku. a, Fiia- Nostoc are constantly found in the tissues 

 ment with two heterocysts (fc), f certain Hepaticae, in Lemma, and in the 



anda large number of spores (sp); r n j n i ■ -i i 



b, isolated spore beginning to roots of °y cas and Gunnera j _ and similarly 

 germinate; c, young filament a species of Anabaena occurs in Azolla. 

 developed from spore. (After Especially interesting are the floating 



BORNET, X 650.) , t J.V. n l i • i. • • 



forms of the Uyanopliyceae, which rise in 

 quiet water to the surface, and collect there in large masses. In 

 the protoplasm of the cells of these species (e.g. Gloeotricha echinulata, 

 Anabaena flos aquae, of fresh-water lakes) are found numerous vacuoles, 

 which are filled with gas and render it possible for the Algae to float 

 on the surface of the water. 



Order 2. Sehizomyeetes (Fission-Fungi, Bacteria) 



The Fission-Fungi differ from the Fission-Algae principally 

 through the absence of an assimilating green pigment in their cells. 

 In them, too, no cell nucleus has as yet been found, although, according 

 to Hegler, a cell nucleus is present in certain species which he investi- 

 gated. Their protoplasm is colourless and always enclosed by thin 

 cell walls. In a condition of plasmolysis, induced by means of a 

 salt solution, the protoplasm becomes contracted, and shrinks from the 

 cell walls, from which it may be concluded that within the cells of 

 Bacteria there is a sap cavity surrounded by a peripheral cytoplasmic 

 layer. Like the Fission-Algae the Fission-Fungi occur under a great 

 variety of forms. The latter, however, are of a much smaller size, includ- 

 ing in fact the smallest of known living organisms. The spherical cells 

 of Micrococcus prodigiesus, which develops on cooked potatoes, bread, 

 milk and meat, and is distinguished by the formation of a blood-red 



