INSECT POWDER. 29 



arate the disc and ray florets, the achenes and bracts, j^rindin^ them 

 separately to the average fineness of a commercial powder. A study 

 of these powders ground from the separate parts of the flower head 

 will enable one to readily recognize them in a commercial sample. 

 Powders ground from closed and open flowers should also be ex- 

 amined. The closed-flower powder is rich in the spiny, 3-pored 

 pollen grains, and should not contain an excessive amount of scler- 

 enchymatous tissue. The presence of considerable sclerenchyma- 

 tized tissue usually indicates very mature (open) flower heads. The 

 powder of open flowers does not contain as much pollen, but tissues 

 from the achene are present in appreciable amount (PL IV, figs. 

 1 and 2). 



The powder to be analyzed microscopically should be thoroughly 

 mixed. This is best done by spreading the sample upon a sheet of 

 white paper and mixing the powder with a spatula. Flattening 

 the powder out upon the paper often reveals the presence of whole 

 unground pieces of material which can be transferred to a micro- 

 scopic slide and examined. After mixing, a composite sample is 

 taken from various parts of the sample. A small amount of the 

 powder is placed upon a microscopic slide, a drop or two of distilled 

 water added, and the cover glass adjusted. If examination of the 

 water mount reveals the presence of any foreign starch, a small 

 amount of a solution of iodin in potassium iodid is drawn under the 

 cover glass. This reagent stains blue any starchy material that. may 

 be present. For further examination a small portion of the powder 

 should be mounted in chloral hydrate solution and gently heated over 

 the flame. This solution serves to dissolve any starch that may be pres- 

 ent, and clears the tissues generally. Until the microscopist has 

 become thoroughly familiar with the Pyrethrum tissues, standard 

 samples ground from the various parts of the flower head should 

 be kept on hand for comparative study. 



Siedler (258) employed phloroglucin and hydrochloric acid in de- 

 tecting the presence of lignified tissues (vanillin reaction). On ap- 

 plying these reagents to disc-flower powder very little lignified tissue 

 was evident, although pollen grains and fragments of papillate cells 

 were numerous. The powder from the involucre showed a large 

 number of woody elements, isolated vessels, thick-walled prosen- 

 chyma cells, scleroids, and pitted parenchyma cells. The short- 

 stalked T-hairs were characteristic of this powder. The ray-flower 

 powder exhibited very little lignified tissue, but a large number of 

 papillate fragments, the cuticle layer, and large epidermal cells 

 which were characterized by their striated surface. The powder 

 from the receptacle showed small, yellowish-brown cells which did 

 not give the vanillin reaction. Thin-walled, porous cells were nu- 

 merous, also lignified prosenchyma cells and large isolated vessels. 



