272 TYPICAL FLOWERING PLANTS 



the leaves to the air and light, carries water and food 

 materials gathered by the roots to the leaves, and distributes 

 liquid foods to all parts of the plant. 



LABORATORY STUDY OF A BEAN STEM 



Make a cross section of a bean stem and find (a) the central pith; 

 (b) the woody ring surrounding it; and (c) the outer green bark and the 

 epidermis. Split a stem lengthwise and identify these parts. Stand the 

 cut-off end of a stem in red ink for a few hours ; then cut across and 

 lengthwise, noting that the woody tissue is stained red. Compare the 

 stem with the root. 



209. The Bean Leaves. — A bean leaf consists of two 

 parts : the stalk or petiole (Latin, petiolus, fruit stalk) by 

 which it is attached to the stem, and the broad, green part, 

 the blade. Petioles are longer in some parts of the plant 

 than in others. Where are the longest ones ? What 

 reason can you give for this? 



The blade of a leaf is in three parts, each of which has 

 a prominent rib entering it from the petiole. From the 

 rib many small branches extend to all parts of that division 

 of the blade. The vascular bundles, or veins, are of use 

 to the leaf, not only in carrying water to it from the root 

 and food back to the root from the leaves, but also in giving 

 firm support to the soft parts between them. 



A leaf like the bean, which has many small veins running 

 together, is called a net-veined leaf. All dicotyledonous 

 plants have leaves with net veins. 



A section through the blade of a leaf shows several dis- 

 tinct parts (Figure 265). The outermost layer is the epi- 

 dermis, a layer of cells without much color, which serves 

 as a protective skin. Below the epidermis is a layer of 

 brick-shaped cells placed on end. These are called the 

 palisade cells. They contain green coloring matter (chloro- 

 phyll) which is held in small bodies called chloroplasts, a 



