102 ESSENTIALS OF BOTANY 
veins proceeding from a midrib and thence extending to 
the margin, as shown in Fig. 66. 
120. Occurrence of Netted or Parallel Veining. — The stu- 
dent has already, in his experiments on germination, had 
an opportunity to observe the difference in mode of vein- 
ing between the 
leaves of some 
dicotyledonous 
plants and those 
of monocotyled- 
onous plants. 
This unlikeness is 
somewhat general 
throughout these 
groups of flower- 
ing plants. What 
is the difference? 
The polycoty- 
ledonous pines, 
spruces, and other 
coniferous trees 
have leaves with 
but a single vein, 
or two or three 
parallel ones, but 
in their case the 
veining could hardly be other than parallel, since the needle- 
like leaves are so narrow that no veins of any considerable 
length could exist except in a position lengthwise of the leaf. 
The fact that a certain plan of venation is found mainly 
in plants with a particular mode of germination, of stem 
structure, and of arrangement of floral parts, is but one 
Fic. 67. The Fall of the Horse-Chestnut Leaf. 
