THE STEM. 



33 



the regular deposition of wood, and would interfere more or 

 km with the regular formation of bark, especially toward the 

 top of the stem. This is the case with monocotyledonous arbo- 

 rescent stems. * 



61, If we make a longitudinal section of a stem of the dwarf 

 Palmetto, we shall observe the following appearances. We find 

 it composed of numerous fibers, interlacing in all directions ; 

 but the general direction of the threads, if we commence at 

 the top, is toward the center, where 

 thev curve toward the circumference, Fi e- ?i. 



A transverse section 

 of a portion of the 

 Yucca gloriosa, from 

 the center to the cir- 

 cumference. 



Transverse section of a fibro- 

 vascular bundle of a mono- 

 cotyledonous stem. 



Longitudinal section of a 

 nocotyledonous stem. 



Fig. 27. The point where the bundle approaches nearest the 

 center is where the base of the leaf has its origin, and sends out 

 bundles toward the circumference. The curve from that point 

 to the base of the leaf is the track that the base of the leaf has 

 taken in its growth. These bundles are composed of woody 

 fiber, tubes, and spiral vessels (Fig. 26), toward the top, or nearest 

 the leaf, and of tubes and woody fiber toward the bottom, and 

 ending in woody fiber only. 



62. All the leaves have their origin at the center of the stem 

 at the top, around the base of a central vesicle. As new leaves 

 are formed and raised up, the older ones are pushed out by the 

 deposition of cellular matter, and come to the lateral surface of 

 the stem, and then all the new matter goes down on the out- 

 side, like a dicotyledon, and forms wood and bark. 



63. All monocotyledons are constructed on the same general 

 principle, and most of the variations are explicable by the greater 



61. What is the appearance of a longitudinal section of the dwarf pal- 

 metto ? What is the point where the bundles approach nearest the center ? 

 What is the curve from that point to the base of the leaf i Of what are these 

 bundles composed? — 62. Where do all leaves have their origin?— 63. What 

 5b said of the construction of monocotyledons \ 



2* 



