CLAWSON: ANATOMY OF JANUSIA. 191 



Material was mascerated with nitric acid and potassium 

 chlorate, and also with chromic acid. The former proved 

 superior for the wood fibers and the wood parenchyma, but the 

 latter gave better results for the bast fibers. 



All sections, except those cut free-hand with the razor, were 

 cut on the rotary microtome, the material being embedded in 

 paraffin. Bismark brown was the main stain used, though 

 hsematoxylin, alcohol safranin, and chloral hydrate safranin 

 were used. 



The leaves were bleached by a method worked out in this 

 laboratory by Mr. Peace. An account of this method is given 

 in the Plant WorUI. April, 1910. Good results were obtained 

 in getting the venation by staining these bleached leaves with 

 chloral hydrate safranin. It was also found to be an advan- 

 tage to use a second stain, Bismark brown, for the study of 

 the epidermis and stomata. In making detailed study of the 

 pits in the stem, dilute glycerine was used for a mounting fluid, 

 but permanent mounts were made in Canada balsam. 



THE STEM. 



The pith in the young stem occupies about one-fourth of the 

 diameter of the entire stem (fig. 1). In the older it becomes 

 much smaller (fig. 2). In the young stem the pith is made up 

 of thin-wall cells, elongated vertically, the wall of which gives 

 the cellulose reaction with c. z. i. The marginal pith cells 

 vary in size, averaging .015 mm. in breadth, and from .074 mm. 

 to .185 mm. in length; while the mid-pith has larger cells, 

 which are not so regular in shape. These average about 

 .03 mm. to .045 mm. in diameter, being in length about the 

 same as those of the margin. 



In the marginal pith cells is found a granular, reddish- 

 brown substance which is insoluble in water, chloroform, alco- 

 hol, xylol, chloral hydrate, hydrochloric acid, and hydrofluoric 

 acid. It is not aft'ected by^atiy of the stains used in this work. 

 With ferric chlorid it reacts and gives a black color. From 

 this reaction it seems that it is a tannin of some kind. It is 

 not a pure tannin, as this is soluble in alcohol at 85 sp. g. This 

 material was passed through alcohol from 20 per cent to 98 

 per cent. Its reaction with ferric chlorid, when compared 

 with the reaction of tannin in Sambucus, was found to be 

 identical. In the older stem the pith cell walls become much 

 thicker, and the cells become longer. They are filled with 



