262 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1920. 



Table 7. — Soil reactions of ferns of woods and simwps. 



Name. 



Schizaea pusilla 



Lygodium palmatum 



Osmunda regalis var. spectabilix 



cirmamomea 



Claytoniana 



Pteretis nodulosa 



Onoclca sensibilis 



Dennstcdtia punctilobula 



Wood wardia areolata 



Virginica 



Pteridium latiusculuni 



Adiantum pedatum 



Polystichum acrostichoides 



Brannii 



Athyrium angustifolium 



acrostichoides 



asplenioides 



angustum 



Dryopteris= Aspidium = Thelypteris 

 (includes Phegopteris). 



Dryopteris Theiypteris 



simulata 



novoboracensis 



Linneana 



Phegopteris 



hexagonop tera 



marginalis 



Goldiana 



var. celsa 



Filix-mas 



cristata 



var. Cliutomana. 



spinulosa 



var. intermedia . 

 var. americana. . 



XBoottii 



marg. X crist 



Reactions. 



No. of 



tests. 



300 + 100 30+ 10 3+ 1 3+ 10 30+ 



X 



AA 

 AA 



A 



A 



I 



C 



I 



I 

 AA 



A 



A 



C 



I 



c 



c 

 I 

 I 

 I 



I 



AA 

 I 

 I 



I 

 I 

 I 

 C 

 AA 

 C 

 I 

 I 

 I 

 I 

 A 

 I 

 C 





Note to Table 7. — None of these species appoars to have been studied by Arrhenius, in Sweden, but it is 

 interesting to note that Pteridium aquilinum, the European relative of our P. latiusculum, was found by 

 him to have a similar range in specific acidity, from 30+ to 3+ . 



Soil reaction and geographic range. — From the foregoing tabula- 

 tion it will be seen that the ferns of woods and swamps are, on the 

 whole, less particular than the rock ferns as to their soil reactions; 

 in but a single case, Dryopteris Goldiana and its variety celsa, are 

 closely related plants sharply contrasted in optimum reaction. It is, 

 however, noteworthy that the peculiar relation found to exist among 

 rock ferns — the favoring of acid soils by southern species and of 

 circumneutral soils by northern ones — is likewise well marked in the 

 present series of plants. As the same sort of relation appears to hold 

 also with other plants than the ferns, in particular with the native 

 orchids, it is sufficiently definite to justify inquiry into its probable 

 origin. 



