262 



XX. STRUCTURE OP THE THALLOPHYTA. 



of the vegetative cells dark brown, of the heterocysts not quite so 

 deeply. The grains in the vegetative cells are not very distinct in 

 this reagent, but show up very clearly in preparations examined 

 in concentrated picric acid. 



Quite similar is the structure of the threads in the olive-green 

 lobed gelatinous masses, sometimes found in great masses on 

 damp paths, and which belong to Nostoc ciniflonum, Tournefort 

 (commune, Vauch). The jelly mass, in this case, is due to the 

 swelling of the outer gelatinous wall of the threads. 



Oscillaria. In examining any terrestrial form of Vaucheria, par- 

 ticularly that collected from flower-pots, we meet with Oscillaria, 



likewise belonging to 

 the Schizopbyta (splitting 

 plants), in closest affinity 

 to the Nostocaceae. They 

 are found, moreover, 

 almost everywhere in 

 standing water, on muddy 

 ground, etc. Their pre- 

 sence is often betrayed 

 by an unpleasant muddy 

 smell. Cultivated in ves- 

 sels, they creep in part to 

 the walls of this, over the 

 surface of the water. They 







FIG. 100. A, Oscillaria princeps / B, Oscillaria 

 Froelichii ; a, ends of the threads ; b, piece from 



the middle of the thread ; in B, b, the granules 

 collected against the partition walls ; in A, c is a are nearly straight, or may 

 dead cell between two living ones. -i n j.i j 



be even coiled threads, 



coloured from blue-green, verdigris-green, olive-green to brown ; 

 can, however, be colourless, and are often distinguished by active 

 motility. The threads are free, or enclosed in a gelatinous sheath. 

 They can be inserted individually, or in numbers, in such a sheath. 

 The sheaths arise from the gelatinous outer layers of the membrane 

 of the threads ; where these layers become diffluent, the sheaths 

 are wanting. The threads are divided by cross partition walls into 

 short disk-like cells. The partition walls in some species can be 

 seen very easily, in others with great difficulty. The cell-contents 

 consist in a hollow cylindrical chromatophore applied to the cell- 

 wall, -and a granular interior. Neither in the Nostocaceae nor 

 Oscillatorieae has a structure like to the nucleus of other organ- 

 isms been determined to exist, unless the whole granular inner 

 body be considered comparable to it. The threads can be fixed 



