CHAPTER XXXIX 



STRUCTURE OF STEMS AND ROOTS 



483. There are two main types of stem structure in 

 flowering plants, which have their differences based upon 

 the arrangement of the fibro-vascular bundles. These types 

 are endogenous and exogenous. 



484. Endogenous Stems. — In endogenous stems, the 

 vascular bundles are irregularly scattered through the funda- 

 mental tissue of the stem (Fig. 452), and are not arranged 

 in circles about a common center. These plants are mono- 

 cotyledons. The bundles are not -parallel with each 

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

 Fig. 453 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 that 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 

 climate are many ex- 

 amples, such as greenbrier, 

 Indian corn, asparagus, 

 grasses, orchids, iris, and 

 cat-tail. 



485. To study arrange- 

 ment of bundles in corn: 

 ( Jut thin sections of a small 

 corn stem that has been 

 preserved in alcohol. Stain with hematoxylin'; or the sections 

 may be examined first without staining. Examine with the 



(285) 



452. Cross-section of oom-etalk, showing 

 the scattered fibro-vascular bundles. 

 Slightly enlarged. 



