234 NODE-FORMATIONS. [BOOK i. 



by the study of an Oak or Lime Tree, but had been ex- 

 tended to various types of other families. I believe it 

 would not be difficult for me to prove that all the modi- 

 fications of woody tissue in ferns occur in every essential 

 point among Spurgeworts (Euphorbiaceae) or Indian Figs 

 (Cactacese) . 



b. Whenever woody bundles pass off into an organ on the 



circumference, they must decussate with the parts which 

 are formed afterwards, and on the outside of the point 

 of departure. This is self-evident, and, so far from being 

 a peculiarity of growth in Monocotyledons, it alone 

 might have led to the conclusion that what is called 

 Endogeneity has no existence. But it is most strikingly 

 apparent in the separate limited woody bundles of Mono- 

 cotyledons ; although well enough in other cases, as for 

 instance in old Melocacti, Echinocacti, and Mammillarise. 



c. But the most important circumstance of all must be 



taken to be whether the interfoliar parts are developed 

 longitudinally or otherwise. In the first case, all the 

 new parts originate upon the surface, (whether they are 

 new woody bundles or an extended development of old 

 ones), and add to the thickness of the stem, without its 

 length being increased by these additions. It is other- 

 wise when the interfoliar parts are undeveloped. In 

 such cases, my observations show that from the period 

 of germination, or the formation of a node, the force of 

 growth not being able to take effect lengthwise, widens 

 each succeeding internode more and more until a cer- 

 tain period, so that every internode projects somewhat 

 beyond that which preceded it, and thus the original 

 lateral surface is converted into a lower surface. A good 

 example of this, is the development of bulbs, and of 

 Melocacti. This increase in size of the internodes goes 

 on only until the plant has formed a sufficiently broad 

 basis. Afterwards, the new internodes cease to expand 

 beyond the old ones ; and a stem appears gradually in- 

 creasing in height, but not in thickness, the interfoliar 

 parts, successively added to each other, resembling hollow 

 cones. A renewal of gradual expansion of the inter- 



