Elementary Plant Physiology. 



15. External force exerted in growth. — The en- 

 largement and change of form of an organ during growth is 

 accompanied by a display of energy the 

 amount of which becomes manifest when 

 some mechanical resistance is encountered. 

 Place as many germinated peas or beans as 

 possible on the surface of closely-packed sand 

 in a pot, and cover to the level of the brim 

 with sawdust or loose soil. Lay a board or 

 sheet of glass over this pot, and place a weight 

 of a few grams on it. Prepare three other 

 pots in the same manner, with increased 

 weights. Note the lifting power exerted by 

 the shoots as they emerge from the soil. 

 Similar action may be observed in the emer- 

 gence of seedlings from the soil. Some buds, 

 shoots, and leaves have a pointed tip suit- 

 able for piercing the soil, and may even 

 bore through the roots and runners of other 

 plants in their upward growth (Fig. 12). 



16. Growth of a fruit — Train a 

 vine of a pumpkin, squash [Ci/curbita'), 

 or gourd so that a branch bearing a young 

 fruit may be brought under cover or 

 indoors, and the fruit placed on the pan 

 of a druggist's balance of sufficient capa- 

 city. Adjust the stem so that it will 

 bend easily, to allow the movement of 

 the arms of the balance upward and down- 

 ward. Equalize the balance by placing 

 weights on the empty pan. Repeat the 

 process several times daily, keeping record of the amount 

 of weight added to the free pan to balance the increasing 

 fruit. If the apparatus can be attended until late at night. 



Fig. 12.— Leaf of 

 Erythronium which 

 has pierced a twig 

 A in its upward 

 growth through the 

 soil, the surface of 

 which is indicated 

 by the dotted line 

 B, After Bessey. 



