THE STEM AND THE LEAF 
71 
the fibrovascular bundles connecting it with the stem. The im- 
portance of this is clear from what has already been said 
Fic. 52. Top view of ver- 
tical shoot of syringa 
(Philadelphus) 
The leaves are arranged in 
pairs, and each pair over- 
lies the spaces between the 
pair immediately below it. 
One fourth natural size 
(sect. 837) about photosynthesis as a 
process of food-making in which the 
elements of water from the soil and of 
carbon dioxide from the air are brought 
together in the leaf to form sugar and 
starch. 
Have the veins of the leaf other uses 
besides their function as conveyers of 
water? Explain. 
69. Alternate and opposite arrange- 
ment of leaves. When a leafy apple 
twig (fig. 51) is compared with one of 
maple or box elder, it is evident that 
the former has its leaves arranged in a 
spiral order, while the latter bears its leaves in pairs. One 
leaf of each pair is on 
the opposite side of 
the twig from its mate, 
and a leaf of each 
pair covers the inter- 
val between the two 
leaves next above or 
the two leaves next be- 
low (fig. 52). Leaves 
borne in spirals are 
said to be alternate, 
and those in pairs, 
like maple leaves, are 
said to be opposite. 
The spiral arrange- 
ment is much the 
commoner, being char- 
acteristic of most herbs, 
and fruit trees. Some 
Fic. 58. Top view of a horizontal shoot from 
the shrub shown in figure 52 
The leaves spring from the branch in the same 
order as do those of the vertical branch, but by 
a twisting of the leafstalks the blades are made to 
lie in a nearly horizontal position, and thus secure 
abundant illumination. One fourth natural size 
most shrubs, and very many hard-wood 
of the most familiar opposite-leaved 
