CHAPTER XXXIV 



STRUCTURE OF STEMS AND ROOTS 



420. There are two main types of stem structure found 

 among flowering plants, which have their differences 

 based upon the arrangement of the fibro- vascular bundles. 

 These types are endogenous and exogenous. 



421. ENDOGENOUS STEMS. Plants with this form of 

 stem are the monocotyledons. The vascular bundles are 

 irregularly scattered through the fundamental tissue of the 

 stem (Fig. 399), and are not arranged in circles about a 

 common center. The bundles are not parallel ivith each 

 other and are not of the same size throughout their length. 

 Fig. 400 shows the direction often taken by the bundles 

 in the stem. On the exterior there is either an epidermis 

 or a false rind. The only trees which have this kind of 

 stem are natives of the tropics or of warm countries. The 



palm is one of them, and 

 these stems are sometimes 

 called the palm type. In 

 our own climate we find 

 many examples, such as 

 greenbrier, Indian corn, 

 asparagus, grasses, or- 

 chids, iris, and cat -tail. 

 To study arrangement of 

 bundles in corn: Cut thin 

 sections of a small corn 

 stem which has been pre- 

 served in alcohol. Stain with hematoxylin. Examine 

 with the low power, and make a sketch showing the 



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399. Cross-section of corn-stalk, showing 

 the scattered fibro-vascular bundles. 

 Slightly enlarged. 



