Page:First course in biology (IA firstcourseinbio00bailrich).pdf/90



horizontal branches are interesting in this connection. 46. Note the enlargement at the base of a branch, and determine whether this enlargement or bulge is larger on long, horizontal limbs than on upright ones. Why does this bulge develop? Does it serve as a brace to the limb, and is it developed as the result of constant strain? 47. Strength of stems. The pupil should observe the fact that a stem has wonderful strength. Compare the proportionate height, diameter, and weight of a grass stem with those of the slenderest tower or steeple. Which has the greater strength? Which the greater height? Which will withstand the most wind? Note that the grass stem will regain its position even if its top is bent to the ground. Note how plants are weighted down after a heavy rain and how they recover themselves. 48. Split a cornstalk and observe how the joints are tied together and braced with fibers. Are there similar fibers in stems of pigweed, cotton, sunflower, hollyhock?

What are roots, and what stems? Has the plant more than one kind of stem? more than two kinds? Explain.