7 8 The Scott is Ji Naturalist. 



or two cautions as to the use of the reagents employed towards 

 the discrimination of species, and 



i st, as regards K and J. 



In those instances where K gives an orange or red reaction on 

 the medulla, the faintest trace of a solution of K on the quill or 

 stick of ivory used in the application of the reagents, before dipping 

 it into the solution of Iodine, will serve to develop at once a 

 beautiful vinoso-violascent colour, whereas, if the quill or ivory 

 had been previously entirely free of K no reaction would have 

 ensued, or, as the case may be, only the usual blue reaction. 



2nd. The solution of Iodine requires to be frequently renewed 

 in order to get the reactions developed, otherwise, apparent dis- 

 crepancies will result, in other words, a solution of Iodine retained 

 for a length of time, and especially if exposed much to sunlight, 

 besides becoming weakened, will often prove powerless as a 

 reagent, where previously a characteristic blue with its consequent 

 violaceous tint had resulted. It cannot be denied that the re- 

 actions by Iodine on the medulla are somewhat uncertain even 

 when every care has been taken in the preparation of the solution. 

 How to account for this has engaged my attention for some little 

 time, but I have failed to arrive at any satisfactory explanation of 

 the difficulty. Probably chemical changes in the constitution of 

 the gelatine will ultimately account for such differences in the re- 

 actions — changes induced during the process of decay and disin- 

 tegration. The abstraction or rather addition of the elements ot 

 water in starchy compounds is well known to occur under such 

 very slight differences of external conditions as are implied in 

 varying degrees of moisture and temperature, and it is not unlikely 

 that an explanation may be afforded by experimenting in this 

 direction. Be this as it may, I have no hesitation in stating my 

 convictions of the importance of attending to chemical reactions 

 as factors in the discrimination of such simple structures as 

 Lichens. 



The opponents of this means of investigation are certainly in 

 the minority, and as time goes on their ranks are thinned by 

 desertion. Even Professor Tuckerman of Amherst, U.S., one of 

 the most inveterate enemies of such tests is fain to seek, in more 

 than one instance, an additional characteristic for his species by 

 means of such reagents, more especially when the true botanical 

 distinctions are of somewhat doubtful significance. It is true he 

 usually appends a note by way of excuse for so acting, for the 

 purpose, it may be, of keeping up an honourable consistency. 



