i6 



THALLOPHYTES. 



The cells which lie immediately above the basal cell form a resting spore ; it becomes 

 thicker, and at the same time lo to 14 times as long as thick, of cylindrical form and with 

 rounded ends, and now forms, so to speak, the handle of the whip-shaped filament ; its 

 contents become denser, and darker from numerous granules, without, however, losing 

 the bluish-green colour, and it surrounds itself with a compact firm membrane or sheath. 

 At the commencement of the winter the cultivated plants disappear, only the Spores 

 together with their sheaths remain behind, and commence germinating in January. The 

 cylindrical cell divides first of all into 4, 6, 8, or 12 shorter cylindrical cells ; the biparti- 

 tion is then repeated in all the cells through several generations, until the filament which 

 arises in this manner from the spore numbers from 120 to 150 cells. The cells have 

 already begun to be rounded off, and the filament has become moniliform; as it lengthens 

 it splits the envelope of the spore, or raises up its upper part like a cap, while the lower 

 end of the filament remains in the sheath. With its increase in length the filament 

 decreases in breadth. When it has attained double the length of the sheath, it escapes 

 completely from it, and the terminal cells become pointed. The filament then splits up 

 into from 5 to 7 pieces about equal in length and in the number of their cells ; the pieces 

 place themselves close to one another, until they form a bundle or tuft ; then each piece 

 begins to transform itself into a whip-shaped Rivularia-filament ; one terminal cell be- 

 comes the basal cell ; at the other end of the filament the cells elongate into an articulated 

 hair. Various deviations from these normal processes occur however not unfrequently. 

 The tuft of threads proceeding from a spore now forms a young mass of Rivularia, the 

 threads of which are already imbedded in jelly. The multiplication of the filaments of 

 a young growing mass takes place by apparent branching ; /'. e. one of the lower cells 

 becomes a new basal cell ; the piece of filament lying between it and the old basal cell 

 developes into an independent filament, which places itself beside the mother-filament. 



With respect to colour, habitat, and mode of life, as well as the tendency to form 

 gelatinous envelopes, the Chroococcacese agree with the Nostocaceae ; the diff'erence lies 

 in their cells not being united into filaments. In Synechococcus, Gloeothece, and Apha- 

 nothece, the cells of all the generations elongate and divide in the same direction, and 

 would form filaments if they did not separate from one another. In Merismopoedia the 

 generations of cells divide alternately in two directions, flat plates consisting of one 

 layer being thus formed. In Chroococcus, Gloeocapsa, and Aphanocapsa, the division 



takes place alternately in three directions, roundish 

 families arising which are finally amorphous ^ (Fig. 154). 

 The mass of layers of the softened gelatinous walls of 

 the mother- cell surround the daughter-cells which proceed 

 from it with their gelatinous envelopes which are also stra- 

 tified, and thus form systems of layers enclosed in one 

 another. The relations of growth now pointed out in the 

 case of Nostocaceae and Chroococcacese are repeated, in 

 all essential particulars, in some other groups of very 

 simple Algae, the cells of which contain pure chlorophyll. 

 The peculiar bluish- or brownish-green colour which the 

 Nostocaceae share with the Chroococcaceae, is caused by 

 a mixture of true chlorophyll with phycoxanthine and 

 phycocyanine ; the phycocyanine is diffused from dead 

 or ruptured cells, and thus produces, for example, the blue stains on the paper round 

 herbarium specimens of Oscillatorieae. If the plants are crushed and an extract made 

 with cold water, a solution^ is obtained of a beautiful colour which is blue in trans- 

 mitted and blood-red in reflected light. If the crushed plants, after extraction of the 



Fig. 154.— Mode of cell-division 

 Chroococcaceae. 



^ Niigeli, Gattungen einzelliger Algen. — Braun, Verjiingung, p. 139. — Ray Soc. Bot. and Phys. 

 em. 1853, p. 131. 



2 Cohn, Archiv fiir mikr. Anat. von Schultze, III, p. 12. — Askenasy, Bot. Zeitg. 1867, no. 29. 



