Chemistry

 Chemistry in the 1860s

There are two pages on this website dealing with the major historical episodes from the first century of 'chemical' lichenology. The current page will deal with the beginnings of chemical lichenolgy and the story will continue with CHEMISTRY AFTER THE 1860s. Much of the information is taken from the paper cited in the following reference button. About 10 of its pages are devoted to a historical background.

Nylander & Leighton

Systematic chemical testing started in the mid 19th century with William Nylander (1822-1899), working in Paris. There had been some earlier observations of colour reactions when certain chemicals were applied to lichens but Nylander tested numerous species in a methodical way and showed that chemistry had potential in lichen identification and taxonomy. Three papers published by Nylander in 1865-1866 are generally considered as the starting point for the use of chemical tests in lichenology. In these he reported a number of findings regarding the effects of iodine solutions (signified by I in modern literature), bleaching powder (signified by C) and potassium hydroxide (signified by K), but he had published some observations about the effect of I as early as 1853. He also noted that it was important to record where in a lichen the I, C or K reagents produced a reaction. For example, in a given species a particular reagent might produce a colour change in the medulla but not in the cortex.

William Leighton in England quickly accepted the usefulness of these chemical tests and also found that applying C after K sometimes gave a reaction when neither C nor K alone did. In 1867 he published the results of his own testing as well as an English translation of Nylander's observations with C and K, which the latter had originally published in Latin. The genus Roccella has long been a source of dye for the clothing industry and Nylander applied hypochlorite of lime (a bleaching agent and hence a C test) to various species in the genus, noting that some reacted with the reagent but others didn't. Moreover any colour change (to red) was confined to the cortex. In summary Nylander (in Leighton's translation) wrote the following in regard to identifying various species in the genus Roccella:

Thus are we now able, with the aid of the hypochlorite of lime, with great facility to separate and distinguish the species of this difficult genus, in which heretofore the determinations have been often uncertain.

The species he was referring to were ones that had already been described by earlier lichenologists based on non-chemical features. Nylander is saying that while those species could be identified by non-chemical means such identifications were at times uncertain and so mistakes were possible. By contrast, according to Nylander, the chemical test would give an easy and unambiguous answer. In this case chemistry was being used simply as an aid to identification of species already defined by their morphological features but Nylander also saw a role for chemistry in the definition of new species. So, for example, chemical differences led Nylander to describe the species Parmelia olivetorum which, in his view was clearly distinct from Parmelia perlata. The former gave a red reaction with C while the latter did not. Once gain, here are his words as translated by Leighton:

The reactive thus demonstrates in the most decided manner, for example, that P. olivetorum...is a species perfectly distinct from perlata, with which it has been hitherto united. Certain organic differences without doubt also afford constant marks of distinction between the two species; but these marks are much less apparent and much more difficult to verify than the chemical differences here noted; so that we must no longer confound them, as has hitherto been done in all the herbaria, since the most inexperienced person is now able to distinguish them by means of the reactive.

The old, heterogenous genus Parmelia has been divided into a number of genera and today Parmelia olivetorum is known as Cetrelia olivetorum, while Parmelia perlata is Parmotrema perlatum (though you will also find it sometimes referred to as Parmotrema chinense, which has been shown to be an incorrect usage and there's more in the following reference button). While Nylander allows that differentiation of the two species may be possible by "organic" (i.e. non-chemical) differences, he thinks such features far harder to discern and therefore less reliable.

In the above two quotations Nylander's words, albeit in Leighton's translation, give an indication of the enthusiasm with which Nylander promoted the use of chemical tests. Though keen on the use of chemistry Nylander was by no means blind to non-chemical features (or characters). If chemical differences were found then other differences should be looked for, as the following extract from Leighton's translation shows:

The chemical characters have also this advantage (as I have noticed elsewhere in speaking of the utility of the different reactions obtained with iodine as characters of Lichens), that we are guided by the differences manifested through the reaction to search with more attention for organic characters; and as a general rule, we shall not fail to find them.

One useful side effect of the discovery of a chemical difference within a species is that it gives incentive to look afresh at that species to see if there are any correlated non-chemical differences. As you will see shortly, ever since the introduction of chemical tests there have been arguments (sometimes quite heated) about their role in lichen taxonomy. However, even many who have allowed no role for chemistry in defining species have been induced to look for correlated non-chemical differences and then use those other features to differentiate species. Studies since the mid1800s have made clear the taxonomic importance of more micro-structures than were used in taxonomy during Nylander's time. Going back to the olivetorum/perlata example one of the correlated structural differences is the presence or absence of pseudocyphellae. A pseudocyphella is a break in the cortex and is discussed on the FORM AND STRUCTURE page. Of those two species olivetorum reacts with C and the upper side of the thallus has pseudocyphellae while perlatum does not react with C and lacks pseudocyphellae. Under low magnification the pseudocyphellae look like tiny white pinpricks and at least one European field guide for amateurs uses this as a means of telling the species apart in the field. The accompanying photo shows part of a herbarium specimen of Cetrelia olivetorum with numerous, white, pinprick-like pseudocyphellae easily visible.

Lindsay's criticisms

The English lichenologist William Lauder Lindsay strongly opposed any reliance on chemistry. In 1869 he published a paper in which he reported on the chemical tests he had carried out on many lichens, including repetitions of tests that had been undertaken by Nylander or Leighton. In Lindsay's view the chemical tests gave no reliable information. The same test, repeated on the same species would not always give the same result and he also reported that when he carried out some of the experiments that had been done by Nylander or Leighton he obtained results different to theirs. Lindsay also wrote that at times Nylander and Leighton contradicted themselves. For example, Lindsay rightly pointed out that Nylander (in Leighton's translation) had written that Rocella fuciformis (with C):

...ordinarily exhibits the curious peculiarity that its thallus is not coloured by the reaction, which on the contrary gives to the soredia of this species the most vivid red colour...

and yet a little later in that same translation Nylander stated that in a fertile specimen of Rocella fuciformis, collected in Portugal:

I have seen some reaction, especially at the extremities of the branches of the thallus.

In commenting on Nylander's and Leighton's work Lindsay included this tart personal jibe:

The papers of these distinguished lichenologists appear to me to illustrate the danger of hyperenthusiasm in matters of science (which are, or ought to be, strictly matters of fact), and the aptitude of even the most experienced observers to be misled by a false scent, by a hobby, or a theory.

Nevertheless, while he thought chemistry might, at most, be of very little value Lindsay accepted that chemical observations warranted being recorded and finished his paper with the following paragraph (with the italics as in the original):

I cannot, then, commend chemical "characters" to the confidence of the lichenologist. At the same time I hold that a botanical diagnosis ought to be based on all characters at the command of the observer, including those which are chemical. And, though I believe that characters drawn from morphology, gynaecology, anatomy and physiology must ever stand in the foreground, it would be wrong in the lichenologist not to avail himself of any assistance that may, in certain exceptional and difficult cases, be supposed to be afforded by chemical reaction in diagnosis. I am very far from desiring to depreciate chemistry as an adjunct to botany in plant-diagnosis; but so far as concerns the Lichens, I believe their chemistry is as yet in far too crude an unsatisfactory a state to warrant us in expecting any assistance that can be relied upon from colour-reaction in the determination of species!

While Lindsay might not want to "depreciate chemistry as an adjunct to botany" the paper's first page has a footnote, part of which reads " I cannot, however, accept the testimony of a chemist on a question of botanical diagnosis".

Why the conflicting results?

Lindsay's was not a superficial paper. It was a detailed report on the results of using a variety of reagents on a wide range of species. So what are we to make of his findings and his conclusions, opposite to those of Nylander and Leighton? In this section I will not present an exhaustive analysis of the conflicting results. Rather I will discuss a few cases to point out some of the issues.

In a case such as Rocella fuciformis the reaction in the thallus of the Portuguese specimen does suggest that a more detailed examination would be warranted to be sure that chemistry was a reliable tool for identification. What of Nylander's differentiation of Parmelia perlata and Parmelia olivetorum? Lindsay wrote that he had not been able to test authentic specimens of Parmelia olivetorum but that he had obtained a pale blood-red reaction in Australian samples of perlata. In view of that result he had:

...no reason to suppose that in this case, exceptionally, chemical reaction furnishes a character sufficient of itself to separate or constitute species.

Lindsay's conclusion is illogical for it avoids the issue. Nylander had said that the prime difference between perlata and olivetorum was the red reaction shown by the latter and that the two species could be confused morphologically. On that basis a logical conclusion would be that Lindsay had shown olivetorum to occur in Australia. If Nylander's approach were to be refuted it would have needed a more detailed and subtle argument about the way species were to be defined. In his very brief treatment of the olivetorum/perlata issue Lindsay is essentially dismissing chemistry a priori, rather than presenting any counter argument. Also, one may wonder what Lindsay was testing when he was using those samples of 'perlata' from Australia. Parmotrema perlatum (Nylander's Parmelia perlata) is common in many parts of Australia and a modern study of the Australian species of Parmotrema confirms that the Australian specimens of Parmotrema perlatum show no colour change with C. Cetrelia is largely a Northern Hemisphere genus but it is interesting to note that Cetrelia olivetorum (Nylander's Parmelia olivetorum) has been found in Australia, though very rarely. In theory it is therefore possible that Lindsay had samples of olivetorum, though probably unlikely given the extreme rarity of that species in Australia. Given that he reported a reaction with C and assuming that he did not have olivetorum, Lindsay must have tested some other species that had been misidentified as perlata.

Such misidentification was potentially a significant problem in correlating the results of chemical tests with species defined morphologically. Species descriptions of the time were often short and could be vague enough to allow two species to be confused. In such a case two people who, in all good faith, thought themselves describing chemical differences in the one species, would have been unknowingly dealing with two distinct species. It was a possibility that Nylander pointed to as a likely explanation for some of the supposed inconsistencies between his and Lindsay's findings and even before Lindsay's paper had appeared Nylander (in Leighton's translation) had warned of the problem:

The analyses of Lichens made by chemists often fail through the neglect of an exact determination of the species, and probably not less often by the mixture of specimens confused together and incorrectly assigned to one single species.

Nylander also wondered if Lindsay had used exactly the same reagents as, with at least one there was the possibility that Lindsay's recipe had been different to Nylander's.

The Finnish lichenologist has written, with regard to I, that "...different formulas and concentrations of iodine reagents have different staining properties...and Nylander only vaguely reported his procedure". It is also known that at times dried material, when rehydrated with water and then tested with I will give no reaction but dried material rehydrated with weak potassium hydroxide, washed with water and then treated with I will give a reaction. If chemical tests are to be used then the test reagents need to be standardised so that comparisons between the work of different people can be compared legitimately and such standardisation did develop later. Finally there was the issue of the quality of the reagent. Solutions incorporating bleaching powder had to be fairly fresh, a point emphasized by both Nylander and Lindsay.

It is interesting to read in Lindsay's 1869 paper that whenever he had obtained different results at different times from the same test on the same specimen (not just the same species):

This must have been due, apparently, to some trivial difference in the reagent or its application, or in the parts of the same thallus operated on. A difference in the degree of concentration or freshness of the reagent, or in the amount of friction employed, would account for all the discrepancies in the results obtained.

I will explain "friction" shortly. For the moment, Lindsay presumably meant his comments about "trivial differences" and so on as a dismissal of the utility of chemistry. On the other hand they implicitly suggest the need for a study into how, for example, different concentrations would affect the results.

It was common to use a glass rod to apply the reagent to the lichen but sometimes the reagent would not adhere to or be easily absorbed by the lichen, so requiring either repeated additions or a rubbing of the surface with the rod (i.e. friction) to help promote adherence and absorption. Nylander also wrote of a more precise method of applying a test reagent:

The instrument I use for applying the reagents is a goosequill sharpened into a point; with this I touch but a very small extent either of the cortical layer (or the apothecia) or of the medulla, observing at the same time the effects of the application through a magnifier.

It has also been pointed out that in some cases where Lindsay reported different reactions within the one species it was almost certain that he had effectively discovered different chemotypes of the one morphological species but without realising it.

The later history...

...is the subject of the CHEMISTRY AFTER THE 1860s page.