58 EASY LESSONS IN VEGETABLE BIOLOGY. 



CHAPTER X. 



ENDOGENS, OR INSIDE-GROWERS. 



1. GRASSES, rushes, lilies, and palms, with similar 

 families of plants, are found in the type of Endogens, 

 Chap. IY, Sec. 5. This term was given to them 

 because it was thought that their woody and vascular 

 fibers grew from the inside, and pushed the earlier- 

 formed bundles of fibers toward the circumference 

 of the stem. More exact examinations have shown 

 that the fibro-vascular bundles grow within the cellu- 

 lar or fundamental tissue, turn first inward toward 

 the center or pith, and then bend outward and pass 

 into the leaves. In grasses the cells of the center dis- 

 appear except at the nodes, (Chap. IX, Sec. 1,) leav- 

 ing the stem hollow. 



2. Endogens are often called Monocotyledons, 

 (Greek monos, one, and Tcotyledon, a seed-lobe,) be- 

 cause the young plant has but a single seed-lobe. 

 Exogens have two seed-lobes, as we may see in a 

 sprouting bean or pea, and are called Dicotyledons, 

 (Gr. die, two.) Acrogens and Thallogens have no 

 seed-lobe at all, but are propagated by cellular spores, 

 and are called Acotyledons, (Gr. a, without.) 



3. In Endogens and Exogens we find a more com- 



