286 



GROWTH 



366. Growth of a Leaf with Parallel Veins. The elongation of 

 a leaf, or its extension in any direction, bears a direct relation to 

 the arrangement of the mechanical tissues. Germinate some 

 bulbs of Narcissus, tulip, or any convenient plant and measure 

 intervals to determine the zone of greatest growth and the rate 

 of elongation, as in 364. * 



367. Growth of a Leaf with Netted Veins. Many leaves attain 

 the major part of their extension, or growth, before unfolding from 

 the bud, and show but little action except placing the lamina in 

 proper position after the bud opens. Select some species in 

 which the newly emerged leaf is but a fraction of the size of the 

 adult form, and make an index mark at the base of the lamina. 



1 2 5 4 9 6 I 8 S » 11 11 11 U 1! 18 VII 19 SO 21 S£ 



Fig. 136. Curve showing relative amount of growth in the terminal portion of a 

 stem of bindweed in 24 hours (see Fig. 135). The basal line is divided into the 

 same number of intervals as the stem, and the amount of elongation of the corre- 

 sponding section of the stem is measured vertically from the point at which the num- 

 ber is placed. The line joining these measurements forms the curve illustrating the 

 relative rates of growth of the regions of the apical part of the stem. After Bon- 

 nier and Leclerc du Sablon. 



Measure exact distance to the tip. Also place a line of dots a 

 cm. apart, at right angles to the main axis. Ascertain daily ex- 

 tension in length and breadth. Determine the regions of maxi- 

 mum growth in both directions. 



368. Course of Growth. The growth of nearly all organs is ac- 

 companied by increase in volume, as well as weight. The activity 

 of the organ in making additions to its living substance, permanent 

 material, or stored food, may be followed by means of devices 

 for making a continuous record of the amount of elongation of 



