246 THE AMERICAN MONTHLY [November, 



" Lac. Cell and Finish " is especially adapted to deep cells, and the 

 Transparent Cements and Zinc White to thin ones, as well as to finish- 

 ing. It is no objection to them that they make very neat and hand- 

 some work. Dr. King will l3e glad to send sample bottles post free on 

 receipt of advertised prices. 



The Examination of Nostoc. 



By H. N. CONSER, 



NEW BERLIN, PA. 



With the pond ooze collected in the search for desmids, one fre- 

 quentlv, and almost certainh' at this season, finds small, bright green 

 gelatinous masses of a millimetre or less in diameter. This is a plant 

 which is worthy of examination. Placing one of these on a slide and 

 examining with low power, it appears to be a capsule of jelly filled 

 with short green threads. This capsule is relatively thick and of con- 

 siderable firmness, so that it needs to be picked apart with needles before 

 the mass can be spread out for examination with higher power. This 

 done, the tlireads which lie in curved and twisted forms resolve into 

 beaded filaments. The cells composing these little rosaries will, on 

 closer examination, be found filled with numerous fine grains, and 

 many of them in a state of division. The larger cells at intervals ax^e 

 of a different kind. The protoplasm in these is homogeneous, nor are 

 they capable of multiplication. These are the heterocysts or terminal 

 cells, so called because the filament is usually terminated by such. It 

 will be seen, too, that these heterocysts differ from the other cells in hav- 

 ing thicker walls and being of yellowish brown color. Now run a 

 little picric acid solution in vuider the cover-glass. The protoplasm 

 will be fixed, and the granules become more distinct. Notice further 

 the little hook on each side of the heterocyst where it joins the line of 

 vegetative cells. Having washed out the picric acid well, applv methvl- 

 green, which is so useful in detecting the nuclei of vegetable cells, and 

 see that all except the heterocysts are distinctly and evenly colored by it. 

 A nucleus cannot here be spoken of. The nuclear substance is, how- 

 ever, present, but in fine grains, evenly distributed. The division of the 

 cells is such as found in other plants of like structure of cell — by con- 

 striction of the cell-wall, which latter, growing as a partition between 

 the two halves, separates them into two united though functionally sepa- 

 rate individuals. 



The plant just considered is A^octus cini.flonu7)i, belonging, with Os- 

 cillaria, to the few Schizophvtes with other than colorless protoplasm. 

 In this case the protoplasm is a bluish green, which gives to the order 

 the name Cyanophyceai. The nostocs are not without interest. This 

 one often appears in great masses by sandy roadsides or garden walks 

 in late autumn after a rain. Many people believe it to fall from the sky, 

 being otherwise unable to account for its sudden appearance. In dry 

 weather it shrinks to a brown film, but retaining its vitalitv expands 

 with the next shower to begin anew its rapid multiplication. Other 

 nostocs are interesting for their symbiotic relation to higher plants, con- 

 stantly occurring in Blasia, one of the liverworts, in the Azolla coro- 

 liniana. and manv others. 



