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THE PLANT WORLD. 
THE “ MONSOON-DUST ” OF THE SOUTH ATLANTIC 
OCEAN. 
The term monsoon is not restricted to the periodic winds of the 
Indian Ocean, but is often applied also to a similar wind that 
blows over the Atlantic Ocean between the coast of Brazil and 
the west coast of Africa. Sailors plying these waters at the time 
of this monsoon are familiar with the phenomenon known as the 
“ Monsoon-dust,” or “ Passatstaub.” There appears over the 
ocean surface a color quite different from the usual ocean hue. 
In quiet weather the surface of the water in the distance, and 
often in streaks, appears to be of a peculiar yellowish or yellow- 
green tint. 
This variation in color from the usual blue-green of the sea in 
Fig. 29. A, a complete colony of Trichodesmium Hildebrantii forma 
Atlantica; B, part of a single filament showing the smaller cell at the 
end at a and a cells which have just divided. (After P. R. Reinsch.) 
quiet weather is quickly recognized by even the “ land lubbers,” 
and has been for a long time a familiar sight to sailors. 
It has been the general opinion that the periodic variation in 
color is due to some pigmented substance floating on the water 
surface, because with the lightest wind the color effect is de- 
