INVASION OF VIRGIN SOIL IN THE TROPICS! 
Duncan S. JoHnson 
(WITH TWO FIGURES) 
This note is concerned with the revegetation of a tropical valley 
which was denuded of plants by a flood and later filled with detritus 
from a landslide. Acknowledgments are due to Messrs. H. A. 
GLEASON, Wittiam Harris, M. A. Howe, E. P. Kui, W. R. 
Maxon, and Percy Witson for the identification of plants collected 
in the Cascade Valley; to E. P. Kriire and Wi1aM Sereriz for 
‘taking photographs of the valley; and to Jonas WALKER, a 
Jamaican collector, for gathering plants growing in the valley in 
December. 
The Blue Mountain region of Jamaica was subjected, in Novem- 
ber 1909, to several days of nearly continuous torrential rains, such 
as apparently occur there only once or twice in a century. On 
November 8, 1909, there was a rainfall of 18.3 inches in 24 hours 
at the Cinchona Station, and this downpour continued into the 
next day, until 27 inches had fallen. The rainfall was undoubtedly 
heavier still on the higher peaks of the Blue Mountains which 
drain into the valley under discussion. 
The floods arising from these tremendous rains caused striking 
changes in the topography, and in the plant covering of many con- 
siderable areas on both the north and the south sides of the Blue 
Mountains. In the first place, many small streams rose two or 
three meters above the normal level, and scoured their rocky 
banks clean of vegetation, aside from larger trees, for many meters 
on either side. In the second place, there were landslides from 
the wooded mountain sides, and especially from the cultivated 
coffee fields, which completely carried away soil and vegetation 
from scores of acres on the south side of the mountains. These 
landslides not only left great scars, showing the bare rock on the 
formerly tree-covered mountain sides and in the coffee fields 
* Botanical contribution from the Johns Hopkins University, no. 70. 
395] {Botanical Gazette, vol. 72 
