EXCURSION ON THE RIO NEGRO. 
335 
plants throughout the whole vegetable kingdom are ar- 
ranged ; laws now recognized by the most advanced botan- 
ists of the day, and designated by them as Phyllotaxis. The 
simplest arrangement in these mathematics of the vegetable 
world is that of the grasses, in which the leaves are placed 
alternately on opposite sides of the stem, thus dividing the 
space around it in equal halves. As the stem of the grasses 
elongates, these pairs of leaves are found scattered along its 
length ; and it is only in ears or spikes of some genera that 
we find them growing so compactly on the axis as to form a 
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Fan Baccaba ((Enocarpus distychius). 
close head. Of this law of growth the palm known as the 
Baccaba of Para ((Enocarpus distychius) is an admirable 
