MR. H. B. GUPPY ON PLA.NT DISPEBSAL. 333 



Meth 



in variis foliis in regione Rio Negro, S. Gabriel, Spruce, nn. 560, 

 572 ; Barra, Spruce, n. 548 ; Panure, Spruce, n. 585. 



Species Haplopyrenul^;, nunc ad Fungos a me relatae, aderant 



4 sequentes a cl. Spruce in reg. Rio Negro lectae. 



61. Haplopyrenula. discopoda, Muell. Arg. in Flora, 1883, 

 p. 273 ; ad San Gabriel, Spruce, n. 563. 



62. Haplopyrenula acervata, Muell. Arg. Lich. Paraguay. 

 n. 239 ; ad San Gabriel, Spruce, n. 476 ; ad Barra, Spruce, n. 457. 



63. Haplopyrenula gracilior, Muell. Arg. in Flora, 1883, 

 p. 273 ; ad San Gabriel, Spruce, n. 480 ; ad Barra, Spruce, n. 446. 



64. Haplopyrexula vulgaris, Muell. Arg. in Flora, 1883, 



p. 273 ; ad Barra, Spruce, nn. 445, 610 ; ad Panure, Spruce, 

 n. 583. 



The Rivay Thames as an Agent in Plant Dispersal. By H. B. 

 Guppy, M.B. (Communicated by W. B. Hemsley, F.R.S., 



A.L.S.) 



[Read 16th June, 1892.] 



In this paper I propose to state briefly the results of observa- 

 tions as to the agency of the Thames, its tributary the Lea, and 

 to a minor extent of the Roding, in the dispersal of plants. 



Not only in autumn, but during the winter v and throughout 

 the spring, these rivers are ever carrying seeds, seed-vessels, and 

 other vegetable drift to the sea. It might well be supposed that 

 the autumnal floods, such as the severe floods of October 1891, 

 would wash these rivers clear of vegetable drift, and that but 

 little would be found in the spring. Such, however, is not the 

 case. The months of January and February have yielded my 

 richest collections both in this and in the preceding year in all 

 these rivers, and the explanation of this fact is to be found in 

 the numerous checks that occur in the progress seaward of the 

 vegetable drift. Winds blowing from the same quarter for a 

 week or two, at right angles to the course of the river, cause a 

 surface-flow across the stream, by which much drift is carried 



