153 BOTANICAL MICROTECHNIQUE. 



when unstained, only by the aid of strong objectives. But 

 with lower powers they stand out clearly when the algae 

 are placed in very finely rubbed India ink, according to 

 the method proposed by Errera (III). For this purpose, 

 enough of the genuine Chinese " India ink" may be rubbed 

 up directly on the slide to give the drop a dark-gray appear- 

 ance, and then the alga to be studied is placed in it. 



No trustworthy statements can yet be made as to the 

 chemical composition of these jelly-masses ; and it need 

 only be said that they give no cellulose reactions either 

 with iodine and sulphuric acid or with chloroiodide of zinc, 

 and that they are always sharply defined against the cellu- 

 lose wall and are not in genetic connection with it. 



A number of observations, made especially by Klebs (II) 

 on the gelatinous sheaths of the Zygnemacece, deserve more 

 detailed notice, as they show that these must possess a very 

 complicated organization. 



279. Klebs first established the fact that the gelatinous 

 sheaths always consist of two different substances, one of 

 which can be extracted with hot water and is pretty deeply 

 stained by certain dyes, like methylene blue, methyl violet, 

 and vesuvin ; while the substance which is insoluble in hot 

 water remains quite colorless with these stains. After 

 staining with one of the colors above named, delicate rods 

 are seen in the sheaths, which often appear united into a 

 fine network at the ends which are directed toward the 

 cell-lumen (cf. Fig. 33, 7). The same structure can also be 

 made visible by other means, especially by alcohol. It is 

 evidently due to the fact that the different substances are 

 unequally distributed in the jelly-sheath. 



280. A further remarkable character of the jelly-sheaths 

 consists in the fact that, after the deposition in them of 

 certain precipitates, for instance, of Berlin blue, these are 

 thrown out, together with a greater or less part of the 

 water-soluble substances of the sheath, with swelling of the 

 latter (cf. Fig. 33, // and ///). This " throwing off of the 

 gelatinous sheath" begins with an accumulation of the pre- 

 viously evenly scattered particles into evident granules (cf. 



