86 FOUNDATIONS OF BOTANY 



which, will be explained later in this chapter, the increase 

 in thickness is strictly limited. Such stems, therefore, as 

 in many palms (Fig. 54) and in rattans, are less conical 

 and more cylindrical than the trunks of ordinary trees 

 and are also more slender in proportion to their height. 



STEM OF DICOTYLEDONOUS PLANTS 



100. Gross Structure of an Annual Dicotyledonous Stem. Study 

 the external appearance of a piece of sunflower-stem several inches 

 long. If it shows distinct nodes, sketch it. Examine the cross- 

 section and sketch it as seen with the magnifying glass or the dissect- 

 ing microscope. After your sketch is finished, compare it with Fig. 55, 

 which probably shows more details than your drawing, and label 

 the parts shown as they are labeled in that figure. Split a short 

 piece of the stem lengthwise through the center and study the split 

 surface with the magnifying glass. Take a sharp knife or a scalpel 

 and carefully slice and then scrape away the bark until you come to 

 the outer surface of a bundle. 



Examine a vegetable sponge (Luffa), sold by druggists, and notice 

 that it is simply a network of fibro-vascular bundles. It is the skele- 

 ton of a tropical seed-vessel or fruit, very much like that of the wild 

 cucumber, common in the Central States, but a great deal larger. 



The different layers of the bark cannot all be well recognized in the 

 examination of a single kind of stem. Examine (a) the cork which 

 constitutes the outer layers of the bark of cherry or birch branches 

 two or more years old. Sketch the roundish or oval spongy lenticels 

 on the outer surface of the bark. How far in do they extend ? Exam- 

 ine (&) the green layer of bark as shown in twigs or branches of 

 Forsythia, cherry, alder, box-elder, wahoo, or willow. Examine (c) 

 the white, fibrous inner layer, known as hard bast, of the bark of 

 elm, leatherwood, pawpaw, or basswood. 



101. Minute Structure of the Dicotyledonous Stem. Study, first 

 with a low and then with a medium power of the compound micro- 

 scope, thin cross-sections of clematis-stem cut just before the end of 



