1 68 TEXTBOOK OF BOTANY 



are separated by a cambium layer, the division of 

 whose cells leads to the growth of the stem in thick- 

 ness. The monocotyledons, as a rule, have the bun- 

 dles in their stems scattered like those of the corn, 

 and form no cambium layer. This is the reason why 

 nearly all monocotyledons have slender stems and 

 remain small plants. A few of them, however, includ- 

 ing some of the palms, have a method of growth in 

 thickness quite different from that of the dicotyledons, 

 which enables them to become good-sized trees. 



b. The leaves of monocotyledons are usually not lobed or 

 divided into leaflets. They are nearly always parallel- 

 veined like corn or lily leaves. The leaves of dicotyle- 

 dons are very various in form, but many of them are 

 lobed like oak leaves, or divided like the leaves of peas 

 and beans. They are netted-veined ; that is, the veins 

 are much branched, as in the cucumber and bean leaves, 

 the branch veins interlacing so as to form a network. 



c. The flowers of monocotyledons most commonly have 

 their parts in threes or multiples of three ; for instance, 

 a lily flower has three sepals, three petals, six stamens, 

 and but one pistil, which, however, is formed by the 

 union of three macrospore leaves ; a staminate corn 

 flower has three stamens ; a pistillate corn flower has 

 only one pistil, consisting of a single macrospore leaf. 

 Dicotyledons commonly have the parts of their flowers 

 in fours or fives, or multiples of these numbers. Thus 

 a cucumber flower has five sepals, five petals, and 

 either three macrospore leaves or three stamens ; 

 but the three stamens seem really to represent five, four 

 of which are united in pairs. The bean, another 

 dicotyledon, has five sepals, five petals, ten stamens, 

 and one 'macrospore leaf. 



d. The embryo of a monocotyledon has one seed leaf; 

 that of a dicotyledon has two seed leaves. 



