GROWTH OF PETIOLES AND PEDUNCLES 285 



of the adaptations by which the plant often cuts off large por- 

 tions of its body under adverse, or seasonal, conditions. 



364, Growth of Stems. Cultivate seedlings of Phaseolus until 

 the stems are several cm. in height and show three or more in- 

 ternodes. Mark each internode into intervals of I cm. by means 

 of India ink lines, and keep under good culture conditions at a 

 temperature of 20 C. Measure the distances between the lines 

 24 and 48 hours later. From the data thus obtained ascertain 

 the regions in which growth ensues, the region of greatest growth 

 and the rates of growth in the internodes of various ages. Plot a 

 curve illustrating these points. To do this, draw a horizontal 

 line one-tenth of the length of the portion of the stem under ob- 

 servation. Divide it into millimeter intervals. Draw a vertical 

 line from the left end representing the actual growth in length of 

 the apical section of the stem. Draw a similar line from the next 

 millimeter interval representing the growth of the second interval 

 of the stem, and also the successive portions of the stem. Join 

 the extremities of these lines and the curve produced will give a 

 graphic representation of the growth of the stem (Fig. 1 36). 1 



Repeat the experiment on a larger plant, and ascertain how 

 many internodes are growing simultaneously. Is the region of 

 greatest growth in the same position in internodes of different ages ? 

 Describe the movements of the region of greatest growth in each 

 internode and also the region of the greatest growth in the entire 

 stem. 



365. Growth of Petioles and Peduncles. Secure a number of 

 rootstocks of some acaulescent plant, such as a violet. As soon 

 as the petioles have attained a length of a few cm. mark off into 

 intervals of a cm. by means of India ink, and measure these inter- 

 vals from day to day to determine the rate of elongation of the 

 whole organ, and the zone of maximum growth. Is the zone of 

 maximum growth always in the same relative position ? Repeat 

 with the scape of Arisaema, Narcissus or the petiole of any con- 

 venient plant. 



1 Bonnier, and Leclerc du Sablon. Cours de Botanique. i: 144. 1901. 



