30 BULLETIN 824^ U. S. DEPAKTMENT OF AGRICULTURE. 



Frequently the analyst is called upon to make an estimation of the 

 approximate quantity of insect flower stems that may be present in 

 a powder. The fragments of stem tissue, occurring to some extent in 

 every insect powder, are readily distinguished from the other tissues 

 present. The stems, when ground, invariably break up into longi- 

 tudinal sections. Cross sections seldom appear in the powder. 

 These long strands of collenchyma cells, fibers, and vascular elements 

 have a characteristic appearance, possessing brushlike or slightly 

 frayed ends, differing very much from the shredded appearance of 

 the fragments of bract tissue. For the purpose of estimating the 

 percentage of stem tissues present in a powder, it has been found 

 convenient to make up standard powders, containing known amounts 

 of ground stem tissues, to be used for comparison with the commercial 

 samples. Mounting the powder in xylol often facilitates the detec- 

 tion of stem tissues. The patches of involucral tissue are invariably 

 quite torn and coarsely shredded, and not in the long, smooth pieces 

 characteristic of the stem tissue. The frait (achene) tissue of the 

 Dalmatian flowers occurs in squarish patches of short, thick-walled 

 sclerenchyma cells, containing numerous crystals, many of them 

 diamond-shaped.. These crystals exhibit a variety of colors under 

 polarized light, and are a means of distinguishing the Persian from 

 the Dalmatian flowers, the Persian flowers lacking these crystals in 

 the achene tissues. 



Microscopically some differences exist between the Persian and 

 Dalmatian powders. As has already been mentioned, the marginal 

 papillae are somewhat different in the two species, although this 

 character would not be recommended as a final means for distin- 

 guishing between the two. The two varieties of flowers are much 

 more easily distinguished from each other in the whole form than in 

 the powder. 



Histology of Powder Elements. 



Powder, when pure, is a golden yellow, turning bright yellow when 

 mounted in potassium hydroxid (or other alkaline) solution. Japa- 

 nese powders appear to be more yellow and aromatic than other com- 

 mercial powders, and assume various greenish or ashen hues, depend- 

 ing upon the amount of stems present. The pure powder possesses 

 more or less of an aromatic odor. If stems are present in appreciable 

 amount, the powder tends to have a characteristic sage or tealike 

 odor. 



Phloroglucin and hydrochloric acid are useful in determining the 

 amount of lignified tissue present. Lignified tissues assume a red 

 coloration with these reagents. (Phloroglucin solution: 0.1 gram in 

 10 cc. of 95 per cent alcohol. Concentrated hydrochloric acid.) 

 Potassium iodid solution of iodin turns starch a deep blue (0.05 gram 



