78 MISSOURI BOTANICAL GARDEN. 
quite convex on the free side, and sometimes protrude into 
the passage as papillae or in balloon-like outgrowths. Their 
secretion is a yellowish resin, which fills the passages in 
sections cut dry and examined in water, but rapidly dis- 
solves when this is replaced by alcohol drawn in at one side 
of the cover glass, leaving a residue of fine emulsion drops 
similar to those formed when an imperfectly anhydrated 
preparation is mounted in Canada balsam. In sections ex- 
amined in water after being cut dry, the contents of the 
secretion passages are traversed by fractures, sometimes 
regularly curved, and their high refractive power gives rise 
to the appearance of a limiting membrane about the indi- 
vidual masses, suggestive of a raised cuticule of the secret- 
ing cells, beneath which, according to Tschirch,* the 
formation of the resins of schizogene passages occurs. In 
observing the solution of the resin on the addition of alco- 
hol, however, the apparent membranes are seen to com- 
pletely disappear at once, and I have not been able to detect 
either cuticular blisters or vestiges of the bases of such 
blisters in these sections after the solution of the resin, nor 
in any of the numerous sections of alcoholic material which 
I have examined. ft 
Just outwards from the situation of this ring of secretion 
passages, each wedge of the hadrom or xylem begins with 
* Berichte Deutsch. Bot. Ges. xi. 201, and Pringsheim’s Jahrb. xxv. 
375. 
+ Some difference of opinion exists as to the nature of the secretion 
within these passages. Van Tieghem and Lecomte (1. c. 182) speak of it 
as a resin, while Heim (Thesis, 176) calls it a balsam. The entire 
group of terpenes, ethereal oils, resins, and balsams, is a difficult one 
chemically, and I do not venture to pronounce on the one now in ques- 
tion further than to say that it is insoluble in water, soluble in cold 
alcohol except for the emulsion residue referred to above, and that Mr. 
Bay, who at my request tested it with the Unverdorben-Franchimont 
reaction to acetate of copper (Poulsen, Mikrochemie, 73; Zimmermann, 
Bot. Mikrotechnik, 89), found that it assumes with this reagent the green 
color characteristic of resins and terpenes. It may be noted that the 
same reagent gives an abundant brown precipitate throughout the bark, 
indicative of the presence of tannin. On the resins see further Tschirch, 
Pringsheim’s Jahrb. xxv. 370. 
14 
