224 BOTANICAL MICROTECHNIQUE. 



alcohol, chromic acid, and picric acid. After fixing with the 

 last-named acid, they may be deeply stained with Hof- 

 mann's blue ; but in dilute alcohol they swell and finally 

 disappear wholly. They are also disorganized by iodine and 

 take a spherical form. 



After stimulation of the leaves the rhabdoids contract and 

 become rounded or fall into several pieces, which become at 

 first lens-shaped, but later always more spherical. 



After longer stimulation the rhabdoids decrease markedly 

 in size ; they are therefore regarded by Gardiner as reserve 

 materials. 



Whether these structures should be simply included with 

 the crystalloids cannot be determined from our present 

 knowledge. 



12. The Acanthospheres of the Characeae. 



397. The acanthospheres,* or ciliate bodies, observed in 

 the cells of various species of Nitella, have already received 

 various explanations (cf. Zimmermann I, 73). According to 

 Overton's recent researches (II), they consist of albuminoid 

 substances which most probably possess a crystalline struc- 

 ture and are partly united with tannins. 



398. For recognizing the presence of tannin in the acan- 

 thospheres, Overton used potassium bichromate, osmic acid,, 

 and staining intra vitam with methylene blue (cf. 201, 203, 

 and 208). He deduced their prote'id nature from their be- 

 havior with iodine and potassium iodide solution, Raspail's 

 reagent, and Hartig's potassium ferrocyanide-ferric-chloride 

 reagent (cf. 224, 227, and 230). He also stained objects 

 fixed with an alcoholic sublimate-solution with borax-carmine 

 and an aqueous solution of fuchsin. The crystalline struc- 

 ture of the acanthospheres is best shown by the use of the 

 former stain and mounting in balsam Tolu. 



The difficult solubility of the acanthospheres in acids and 



* [As I am not aware that any English name has been applied to these- 

 bodies, I propose this Greek equivalent of the German name, Stachel- 

 kugeln.] 



