INSECT POWDER. 29 
arate the disc and ray florets, the achenes and bracts, grinding 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. 
