1859.] HYMENOPHYLLUM. 219 



even temperature encourage its growtli. Tii warmer countries 

 and tropical climates high altitudes are more conducive to the 

 liealthy existence of Hymenophyllum and Trichomanes. Bory de 

 St, Vincent, to whom I shall have particularly to refer, men- 

 tions in his notes on Algerine botany the delightful temperature 

 of the province of La Calle, where a perpetual spring exists, for 

 the centigrade thermometer has never stood below 11 degrees, 

 nor risen above 30 degrees in the shade. The forests of La Calle 

 abound in beautiful Ferns, and v/here he mentions the great 

 height of Osmunda regalis, and the gigantic leaves of the Ivy. 

 He singularly states that the Male Fern, Asjndium Filix-mas, 

 does not occur in Africa ; nor, according to Low's Memoirs of 

 the plants of Madeira, does the genuine Aspidium Filix-mas exist 

 there. Holl, on the plants of Madeira, alludes only to one species 

 of Hymenophyllum, the tunhridgense, growing at an elevation be- 

 tween 2,000 and 3,000 feet. In the Floras of France the species 

 tunhridgense is recorded, and is mentioned as growing on the 

 trunks of trees at Cherbourg. I shall now come to a more im- 

 portant point, the opinion generally entertained by botanists that 

 Hymenophyllum Wilsoni of British botany is none other than the 

 H. unilaterale of Willdenow's 'Species Plantarum,' p. 521. We 

 are aware how very nearly some of tlie exotic Trichomanes and 

 Hymenophylla approach in form and habit of growth ; yet the 

 character and position of the involucres in many species are very 

 different. What may be the true characteristics of the involucres 

 oi H. unilaterale we are in some measure led to conjecture. No 

 descriptive terms can clearly determine the doubts entertained of 

 a species. Accurate drawings of the recent plant, or authenti- 

 cated specimens, should only be advanced as confirmatory of the 

 decision of disputed views. Again, there are difficulties of decid- 

 ing species of exotic Ferns, when reference is to an ill-preserved 

 herbarium, and where accurate notes do not exist of peculiarity 

 of locality and of habit. According to Hooker's ' Species Fili- 

 cum,' H. unilaterale of Willdenow, from a specimen from Mar- 

 tins, proved to be the species H. tunhridgense ; and H. unilaterale 

 of Willdenow, according to description, was H. Wilsoni, but not 

 according to a specimen from Martins. Some years since, being 

 much interested in the affinities of Ti'ichomanes of this country 

 with the forms of Trichomanes alatum and T. radicans of Ja- 

 maica, I had manv communication with that amiable and liberal 



