to2 The Scottish Naturalist. 



which gives a yellow reaction, may be named U. hirsutula. In 

 both I—. 



One very common reaction on the cortical layer of the thallus 

 is K — or f y C yellow more or less pronounced in different 

 cases ; but, accordingly, one that can seldom be made use of in 

 the discrimination of species. It is only recorded in one or two 

 well-marked instances. Of all parts of the stem, that most 

 frequently affected by K (i.e., liquor potassse) is the external 

 medullary layer, composed, as a rule, of fibres more or less 

 arachnoid. The surface of the dense central axis, and the 

 medullary fibres in immediate contact with it, are those parts 

 most apt to be affected by I (Iodine), and, in one section, the 

 substance of the axis itself is affected by the same reagent. So 

 far as my experience goes, C, either alone or in combination 

 with K, does not give a red reaction in Usnea. 



I premise also that U. florida^ hirta (proper), dasypoga, articu- 

 lata, and ceratina have all negative reactions, in the manner 

 stated above, with K and I ; and, so far as my authentic speci- 

 mens from colder climates go, this statement is corroborated. 

 At any rate, one must start from some such basis as this — more 

 especially as no such attempt as the present has been made, so 

 far as has been ascertained. 



Section I. 



Fibrillar medullares K flavescentes ; I caerulescentes, vel vio- 

 lascentes. Soredia K plerumque flavescentia. 



i . Usnea similis Jtoridie, pumila, altit. 2 pollicum vix unquam 

 superans. 



a Usnea intexta. — Thallus pallide cinereo-glaucescens (K — 

 C n\); fibrillar medullares I violascentes. 



Crinan Canal, Scotland. 



(3 Usnea flammea. — Thallus flavescens (K — C Havens). 

 Madeira (J. Payne). 



y Usnea rubicunda sp. nov. — Thallus fere totus rubigineus. 

 England (Mr Holmes). 



8 Usnea sublurida sp. nov. — Thallus similis praecedenti, sed 

 densius dendritico-ramosus, stipitibus et ramis rubigineis 

 at ramulis cinereo-glaucescentibus vel cinereis. 

 In Scotia pas si/n, &c. (J. M'Andrew). 



