STEMS AND THEIR APPENDAGES. 53 



stem. Botanists separate flowering plants into two great 

 divisions — the Endogens and the Exogens, or "inside 

 growers "and "outside growers." As these terms have 

 a special reference to the growth and structure of the 

 stems of plants, it is proper that they should he ex- 

 plained here ; although the difEerences hetween the 

 plants of the two divisions are usually distinguishable in 

 the seed as well. Endogenous stems are not made up of 

 concentric rings or annual layers of deposited matter, as 

 seen in the woody stems of nearly all exogens or outside 

 growers. In the formation of the woody tissues of en- 

 dogens the new material deposited appears to be inter- 

 mingled with the old, and the increase in the size of the 

 stems is principally through " distention or pressing out- 

 ward, and not by the deposition of matter in the form oE 

 layers, such stems consisting of bundles of fibers inter- 

 mingled with or imbedded in cellular tissues. Neither 

 do such stems show the marked distinction between the 

 pith, wood and bark, as seen in those of exogens. The 

 Palms, Ferns, Yuccas, Bamboo, Sorghum and all of our 

 cereal grasses belong to this division of true inside grow- 

 ers. Their seeds are also distinguished by having only 

 one cotyledon or seed-leaf, hence are called monocoty- 

 ledonous plants, the plumule pushing upward from the 

 seed in a columnar form, as seen in the Asparagus, In- 

 dian Com, or the giant Palms of the tropics. In the 

 leaves of these plants we also find that the veins run 

 mostly parallel with the length-^that is, extend from 

 base to point and not branched. 



The exogenous stem has at first three distinct parts, 

 viz., the pith, wood and bark, all readily separable. As 

 the stem increases in size through the deposition of new 

 matter in concentric layers of bundles of wood-cells, 

 the pith is often compressed or entirely obliterated with- 

 out in any manner interfering with the growth of the 

 plant, for the principal office of the pith is to facilitate 



