CO OT. LA.ri)£B LINDSAY ON CHEMICAL BEACTIOX 



duals, of the same species, but in the same specimen at differeut 

 times, or in different parts of it. In the same species reaction 

 may be distinct, faint, or absent. These differences are deter- 

 mined, in great measure at least, by the conditions of growth * 

 or preservation of the specimens (e. g. by their degree of fresh- 

 ness — the interval that has elapsed since they were collected ; 

 the locality of growth in relation to climate, elevation above, or 

 proximity to, the sea ; degree of development in relation to ste- 

 rility, hypertrophy, or degeneration). The differences exhibited 

 by the same species when freshly collected, on the one hand, aud 

 after long preservation in the herbarium, on the other, are fre- 

 quently most marked. Many of the specimens operated on in 

 my experiments were collected so long ago as the beginning of the 

 present century, while none were freshly collected for the pur- 

 poses of the present inquiry. For the reasons formerly stated 

 (p. 40), I have preferred to make use in great measure of the authen- 

 ticated specimens contained in published fasciculi, some of them 

 comparatively old, — contrasting the results with those obtained in 

 specimens from my ow^n herbarium, collected at much later, and m 

 some cases at very recent, dates. But the results so obtained have 

 satisfied me of the non-necessity of engaging in a wider inquiry, 

 or of enlarging the area of experiment by making special collec- 

 tions for the purpose. I haA^e no doubt, however, that still 

 more striking results might have been obtained by operations on 

 freslily collected lichens, in their different stages or conditions of 

 growth. 



III. The frequent uncertainty of result, the irregularity or in- 

 constancy of colour-reaction, even in the same species, renders it 

 impossible to place confidence in cTiemical characters as a means 

 of diagnosing botanical species. ■ 



IV» Even where the phenomena are comparatively constant, I 

 have in no case found colour-reaction assist me either in uniting 

 or separating species or varieties. 



V. The discrepancies that occur among lichenologists making 

 efforts to discover and apply chemical tests for species, occur 

 equally among experimenters on a larger scale, as well as among 

 professional chemists studying scientifically and with no ulterior 

 object the lichen- colouring-matters. Westring, for instance, failed 



* Modifications of reaction according to conditions of growth in the same 

 species are illustrated in the author's 'Experiments' (1st ser.), 1854, Table xx-, 

 p. 35, 



