86 THE LEAF. 
are always connected by simple transverse veinlets. Ex. grass 
lily. 
FIG. 28.— Forms of venation. 1,2, Exogens; 3, Endogen; 4, acrogen. 
3d. Forked-veined, as in the Cryptogamia, when the veins 
divide and subdivide by forked divisions which do not unite 
again. Ex. ferns. 
230. Of the first kind of venation; the reticulate, there are two varieties which 
deserve the most careful attention. The /eather-vemed and the radiate-veined. 
1. The feather-veined leaf is that in which the venation con- 
sists of a midvein, giving off at intervals lateral veinlets and 
branching veinulets. Ex. beech, chestnut. 
2. In the radiate-veined, the venation consists of several 
veins (§227) of nearly equal size, radiating from the base 
towards the circumference, each with its own system of veinlets 
and veinulets. Ex. maple, crow-foot. 
3. In parallel venation, the veins are either straight, as in the 
linear leaf of the grasses, curved, as in the oval leaves of the 
Orchis, or transverse, as in the Canna, Calla, &c. 
§4. FORM OR FIGURE. 
231. That infinite variety of beautiful and graceful forms for which the leaf is 
distinguished, becomes intelligible to the student only when viewed in connection 
with its venation. Since it is through the veins alone that nutriment is conveyed 
for the development and extension of the parenchyma, it follows: that there will 
be the greatest extension of outline where the veins are largest and most numer- 
ous. Consequently, the form of the leaf will depend upon the direction of the 
veins, and the vigor of their action, in developing the intervening tissue. For 
this interesting theory we are indebted to Alphonse De Candolle. 
