— 165 — 



smooth coat, and very cautiously it is to be placed just on the 

 drop on the slide. Generally I have got fine results in this way; 

 but it also happened that the bristles were more or less curved. 



Later on similar stainings have succeeded with other colouring 

 matters e. g. tannic acid fuchsin and tannic acid methylene blue. 



5) The method of dark-ground illumination [Karl Reichert 

 1909] has turned out to be very useful. Its appliance has this 

 particular advantage that it makes it possible to study the bristles 

 alive, and further on it allows just as the preceding method to get 

 a sight of the algæ coenobia in every position. 



The apparatus used was Reigherts Plattenkondensor F. For 

 source of light I have partly used the sunlight, but it is too in- 

 tense and may harm the eyes; partly an electric arc and partly a 

 so-called Grätzinlamp from Reichert. I have in general only used 

 low-power objectives viz. Seibert Nr. II or V. 



In some cases I have got fine results by adding the Zettnow 

 mordant in the modification of K. Reichert to the preparation. 

 [Karl Reichert 1909. Pag. 26]. 



6) In a very few instances I have been able to see the brist- 

 les without any preparation whatever. This has been the case of 

 Pediastrum duplex and simplex but not of any of the Scenedesmus 

 species. 



The figures with no particular remarks are drawn with the 

 aid of the Abbe camera lucida and Seibert Homog. Imm. 1 /ia and 

 Oc. I. 



General remarks. 



The bristles I have found in the species named above are 

 exceedingly thin, hyaline threads projecting from the algæ cells. 

 The thickness is, supposed the bristles are unhurt, equally decrea- 

 sing from the basis to the point, and they are so pointed that it 

 often is almost impossible to ascertain where they end. The thick- 

 ness is as said on the whole not very considerable, measured at 

 the base of the bristles not more than about 0.2 — 0.6 p, perhaps 

 still less; it is however very difficult to measure the thickness not 

 only owing to its smallness, but also because the bristles in the 

 staining-preparations always are more or less cleaved together at 

 their bases and the shorter bristles are often found cleaved to the 

 longer in their whole length. 



