In this series of posts we are going to exam­ine these seemly sim­ple questions:

1. What is the goal and the pur­pose of test­ing of unknowns gen­er­ally? How do we best design a test for marijuana?
2. How is most mar­i­juana test­ing con­ducted in the United States?
3. What is micro­scopic mor­pho­log­i­cal exam­i­na­tion? Is it a “good” test?
4. What is the mod­i­fied Duquenois-Levine test? Is it a “good” test?
5. What is Thin Layer Chro­matog­ra­phy? Is it a “good” test?
6. Is the com­bi­na­tion of all three tests cre­ate a “good” test­ing scheme?
7. Is there a bet­ter way to test for marijuana?

Part 3: What is micro­scopic mor­pho­log­i­cal exam­i­na­tion? Is it a “good” test?

Micro­scopic mor­pho­log­i­cal examination

What is it?

The micro­scopic mor­pho­log­i­cal exam­i­na­tion in short is an exer­cise of botan­i­cal iden­ti­fi­ca­tion using a microscope.

Mechan­i­cally how is it preformed?

A very small amount of the dried unknown is selected. This becomes the sam­ple. The sam­ple is placed on a micro­scopic slide. A drop or two of water is then added to the slide. The slides are exam­ined at vary­ing lev­els of mag­ni­fi­ca­tion and under dif­fer­ent light con­di­tions. What the ana­lyst is look­ing for is two dis­tinct mor­pho­log­i­cal fea­tures. They are look­ing for micro­scopic “hairs” on the unknown. These are cys­tolithic hairs and glan­du­lar hairs. Cys­tolithic hairs are often likened to like lit­tle bear claws in their appearance.

pho­tomi­cro­graphs of cys­tolithic hairs

The sec­ond type of hair is called a glan­du­lar hair. These are fre­quently remarked as look­ing like mushrooms.

pho­tomi­cro­graphs of glan­du­lar hairs

Some tech­niques call for the use of hydrochlo­ric acid after they look for these hairs. A few drops of HCL are added by the ana­lyst. The ana­lyst then looks to see if there is some unspec­i­fied effer­ves­cence under the light of the microscope.

How is the typ­i­cal crime lab­o­ra­tory ana­lyst trained to con­duct this form of testing?

The ques­tion becomes what expe­ri­ence level in botany and tax­on­omy and microscopy does the ana­lyst truly have? Very few under­grad­u­ate pro­grams exist in botany in the United States. Most ana­lysts have on the job train­ing where another per­son who like­wise have no for­mal train­ing in botany or tax­on­omy that instructs them. It also involves the use of a micro­scope. For­mal train­ing in microscopy is required in order to use a micro­scope prop­erly and to prop­erly inter­pret what the human eye sees through var­i­ous pow­ers and light­ing con­di­tions of the micro­scope. At the end of the in-house train­ing, the typ­i­cal ana­lyst can­not typ­i­cally express the fam­ily, the genus and the species that is “mar­i­juana” or at what power and under what light­ing con­di­tions they saw the mor­pho­log­i­cal characteristics.

This sam­ple that is exam­ined under the micro­scope is then dis­carded. All future or addi­tional test­ing is con­ducted on totally dif­fer­ent sam­ples from the unknown.

Is this a ver­i­fi­able test?

It poten­tially is. There is a device that can be linked to the micro­scope to take pic­tures of what the ana­lyst thinks he or she sees. This is called a pho­tomi­cro­graph. In fact the pic­tures above come from just such a micro­scope that is equipped with one. A dig­i­tal cam­era attached to a micro­scope is very com­monly used in sci­ence. They are very mod­er­ately priced. As they are dig­i­tal cam­eras, the cost of pro­duc­tion and print­ing and data stor­age is neg­li­gi­ble. It is fre­quently used in other types of com­par­a­tive exam­i­na­tions such as some higher lev­els of foren­sic firearm or tool­mark iden­ti­fi­ca­tion. I know of no lab­o­ra­tory in the United States that relies upon micro­scopic mor­pho­log­i­cal exam­i­na­tion that uses mod­ern tech­nol­ogy and pro­duces pho­tomi­cro­graphs. In fact, few, if any, crime lab­o­ra­to­ries use the ACE-V (Analy­sis, Com­par­i­son, Eval­u­a­tion, and Ver­i­fi­ca­tion) tech­nique that one would find in fin­ger­print iden­ti­fi­ca­tion using a stereo-microscope and a dou­ble check in real time by a fel­low bench ana­lyst. In essence, the unknown is checked one time, by one per­son with no dou­ble check by another, and noth­ing is pro­duced that proves that the analy­sis was done or that the fea­tures that are reported as present were in fact objec­tively present. There is no proof.

Is there empir­i­cal valid­ity stud­ies that prove that this is a spe­cific and con­fir­ma­tory test?

No. There are no empir­i­cal and robust val­i­da­tion stud­ies that con­clude that this form of micro­scopic mor­pho­log­i­cal exam­i­na­tion even when the two botan­i­cal fea­tures (cys­tolithic and glan­du­lar hairs) are objec­tively present yield a valid opin­ion that the plant exam­ined is def­i­nitely con­tains THC. There are no stud­ies that say the two fea­tures means that there is THC present. In fact, what stud­ies that are out there con­clude that this form of mor­pho­log­i­cal exam­i­na­tion using a micro­scope is per­haps not even selec­tive. In the orig­i­nal stud­ies by Naka­mura, he indi­cated that cys­toliths of var­i­ous types are found in the leaves of a num­ber of dicots. (497). He also indi­cated that the pres­ence of cys­toliths is not diag­nos­tic for a fam­ily, let alone a genus of plants. (497) Naka­mura specif­i­cally noted that cys­toliths are found on a great num­ber of plants includ­ing but not lim­ited to: hops plants (500), oregano (500), lemon thyme (501), sil­ver thyme (501), and rose­mary (501). Naka­mua he specif­i­cally noted 63 “rep­re­sen­ta­tive” species in 13 plant gen­era that con­tain cys­toliths in table 5 of his arti­cle (501) Naku­mura indi­cated that he made NO attempt to pre­pare a com­pre­hen­sive list­ing of species bear­ing cys­tolith hairs sim­i­lar to those found in cannabis “because of the sheer enor­mity of the task to exam­ine 31,874+ dicotyle­dons.” (500). For instance, in one genus found in Table 5 of his arti­cle, the Loasa, he specif­i­cally noted 9 species that had cys­toliths; how­ever, he went on to say that there were actu­ally some 80 species of that genus known to have sim­i­lar hairs. (501). He fully acknowl­edged that his list­ing was not com­pre­hen­sive. So it is accu­rate and very fair to say that the 63 “rep­re­sen­ta­tive” species that have cys­toliths that were noted by Naka­mura in Table 5 of his arti­cle are not an exhaus­tive list. Other stud­ies agree that at least 6 other sub­stances also have hairs that con­tain these two fea­tures (cys­tolithic and glan­du­lar hairs). In terms of the addi­tional step of adding HCL to the sam­ple and exam­in­ing for effer­ves­cence under the light of the micro­scope, it is quite clear that other sub­stances can pro­duce the same effer­ves­cence when a few drops of hydrochlo­ric acid are added to them. For exam­ple net­tles and cat­nip do exactly that.

Some folks main­tain and tes­tify under oath every day in the United States that this unver­i­fied micro­scopic mor­pho­log­i­cal exam­i­na­tion is diag­nos­tic of iden­ti­fi­ca­tion of THC pres­ence in an unknown. There is no sci­en­tific sup­port for this type of testimony.

One thing that every ana­lyst should agree with is that sim­ply because these hairs are present and if they con­duct HCL addi­tion and if there is effer­ves­cence that does not mean that the unknown con­tains THC. This is why they have to do addi­tional test­ing, mean­ing the mod­i­fied Duquenois-Levine and Thin Layer Chro­matog­ra­phy testing.

What is fre­quently not part of any mor­pho­log­i­cal exam­i­na­tion for cannabis is what botanists have noted to be other fea­tures con­sis­tent with cannabis. The sim­pli­fied exam­i­na­tion for the typ­i­cal foren­sic sci­ence iden­ti­fi­ca­tion is pur­pose­fully designed to make this exam­i­na­tion and con­clu­sions from it eas­ier to per­form by non-botanists. As with every­thing in life, the more cri­te­rion attached to qual­ify some­thing the least likely there will be a qual­i­fi­ca­tion. The exam­i­na­tion of cannabis and espe­cially a mor­pho­log­i­cal exam­i­na­tion by untrained botanists should not be made easy. All of the fea­tures that are known to be diag­nos­tic by the world of botany should be used not sim­ply the easy ones. For exam­ple, botanists have noted that that cannabis has ses­sile glands as well as con­tain­ing ser­rated edges of the leaves and com­pound palmate struc­ture mean­ing sev­eral leaflets arise from the same point. The addi­tion of all of the known mor­pho­log­i­cal fea­tures known to true botanists as diag­nos­tic of cannabis would make this exam­i­na­tion more robust and the result more selec­tive than the sim­plis­tic exam­i­na­tion that now per­me­ates the foren­sic sci­ence world.