1898.] of "Connecting Threads" in the Cell Wall. 509 



This may be done either by means of Iodine alone, or by repeating 

 the operation of mordanting and staining one or more times. 

 Intensification with Iodine is accomplished b}^ simply treating a 

 stained section either with a solution containing *1 °/ Iodine and 

 "15 °/ c Potassic Iodide in 5 °/ Sulphuric acid, or with a solution 

 of 5 c / Sulphuric acid saturated with Iodine and then examining 

 the section mounted in one of these reagents. The Iodine forming 

 a black precipitate with the Aniline violet causes the protoplasm 

 and threads to stand out much more clearly than before. The 

 blue tint assumed by the cell wall in consequence of slight 

 staining also disappears, since the Iodine in virtue of its intense 

 affinity for the Violet combines with every trace of the dye. 



When intensification by staining is desired the tissue is 

 mordanted with an Iodine solution, which should be more dilute 

 than on the first occasion of staining. It is then passed through 

 a 5 / o solution of Sulphuric acid and again treated with the 

 Sulphuric acid solution of Gentian violet or Pyoktanin. If 

 again treated with and examined in dilute acid Iodine, the proto- 

 plasm and the threads stand out intensely black and peculiarly 

 clearly. One should mention that when secondary staining is 

 resorted to, a certain amount of precipitation upon the section 

 may occur which may necessitate the use of a brush before 

 examination. 



(5) Mounting. In order to render the violet stain " fast," I 

 mount in glycerine containing a small percentage of Zinc chloride, 

 and still better results may sometimes be obtained when a trace 

 of Iodine is present. The Zinc chloride acts in virtue of its 

 property of forming a dense blue precipitate with Gentian violet 

 and Pyoktanin. The mounting solution may be made as follows : 

 o>? c.c. Glycerine, 60 c.c. of water and 10 c.c. of a 20 °/ solution 

 of Zinc chloride are mixed together. To this is added a flake or 

 two of Iodine and the whole is slightly warmed over a warm bath. 

 Section ■ may be transferred from the above solution into Glycerine 



J ell y- 



The demonstration of " connecting threads " in such structures 

 as the " leaves " of mosses and the like, where the whole organ is 

 implicated and the cutting of sections is either undesirable or 

 difficult, involves considerable modification of the above treatment 

 and is not unattended with many manipulative troubles, by reason 

 of the fact that it is exceedingly difficult to limit the staining to 

 the protoplasm and threads, and to prevent it extending to the 

 walls. 



Successful results appear to depend upon the use of low 

 percentages of Iodine for the killing and still lower for the 

 mordanting. For the swelling I find that a 5 °/ solution of 

 sulphuric acid is sufficient. As the result of an elaborate series 



VOL. IX. PT. VIII. 40 



