130 THE JOURNAL OP BOTANY 



T. contorta (Ditm.) Rost. Tregarrick Mill ; Trenean ; Morval. 



T. decipiens (Pcrs.) Micbr. Frequent. 



T. Bofrytis Pers. Frequent. 



Ollgonema nltens (Lib.) Rost. Grampound (J. M. C). 



Hemifrichia ahiftlaa ( Wigand) Lister. Bodmin Valley ; a single 

 ovoid short-stalked sporangiuras on moss; a puzzling specimen. 



Coriiuvia Herpiila (Wig.) Kost. Grampound (J. M. C). 



Arcyria ferrnginea Saut. Morv^al ; Peneartlitown. 



A. cinerea (Bull.) Pers. Frequent. 



A. pomi^ormis (Leers.) Host. Hall Wood, Pelynt. 



A. denudafn (L.) Wettst. Frequent. 



A. incarnata Pers. Frequent. 



A. nutans (Bull.) Grev. West Looe. 



Perichcena depres.m Libert. ISt. Martin's ; Morval ; Tregarrick 

 Mill. 



P. corticaUs (Batscli) Rost. Not uncommon. 



P. vermicularis (Scliw.) Post. ? Near Looe. 



Dianema depressum Lister. Kilminortli Wood. 



PrototricJiia metalUca fBerk.) Mass. ? Near Looe. 



The above list contains eighty-two species and four varieties. 



PLANT DERMATITIS.— I. 



Bv E. Philip Smith 

 (Botanical Department, Oxford). 



Plant Dermatitis {^Dermatitis venenata of medical writers), 

 that is, diseases of the skin caused bj plant-products, is probably 

 much more frequent in occurrence than is usually supposed, owing 

 to the fact that the eruptions produced so closely simulate one (jf 

 the many forms of eczema, erysipelas, etc., that they are commonly 

 diagnosed and treated as such. A more stringent inquiry into the 

 liistory of the case frequently results in the discovery of evidence of 

 contact with some poisonous plant which has wrought the damage. 

 It is therefore desirable to have sonie knowledge of the plants which 

 are known to have disastrous effects upon the skin of those who 

 come in contact with them, in order that the}^ may be avoided ; and 

 that in the event of accidental aifection, a correct diagnosis may be 

 made. 



Plants causing irritation to the skin may he, roughly speaking, 

 divided into two main groups : tbose in which the active principle is 

 contained in the cell- sap or in latex, and those in which it is secreted 

 by glands or hairs of various kinds, whether over the whole surface 

 of the plant, or localized in some special region. Irritant cell-sap 

 covers a very wide range of phenomena, including those due to 

 poisonous alkaloids, phenols, etc., or to the mechanical action of 

 raphides, which work their way in under the skin and so cause an 

 extreme irritation, which is only increased b}" friction. 



A few t^^pical instances may be taken as examples : — 



I. Perhaps the commonest case of all, and one which is known to 



