Iv ON PLANT LIFE 143 
The “Compass” Plant of the American 
prairies, a plant not unlike a small sunflower, 
is another species with upright leaves, which 
growing in the wide open prairies tend to point 
north and south, thus exposing both surfaces 
equally to the light and heat. Such a position 
also affects the internal structure of the leaf, 
the two sides becoming similar in structure, 
while in other cases the upper and under 
surfaces are very different. 
In the Yew the leaves are inserted close 
to one another, and are linear; while in the 
Box they are further apart and_ broader. 
In other cases the width of the leaves is 
determined by what botanists call the “ Phyl- 
lotaxy.” Some plants have the leaves oppo- 
site, each pair being at right angles with the 
pairs above and below. 
In others they are alternate, and arranged 
round the stem in a spiral. In one very 
common arrangement the sixth leaf stands 
directly over the first, the intermediate ones 
forming a spiral which has passed twice round 
the stem. This, therefore, is known as the 
2 arrangement. Common cases are }, 4, 2, , 
