4t) STRUCTURE AND PHYSIOLOGY OF SEED PLANTS 



EXPERIMENT XXIII 



What effect does loss of water have on the firmness of plant 

 tissues ? How long does it take for the water to be restored ? 



A. Allow a fuchsia or a hydrangea^ which is growing in a 

 flowerpot to wilt considerably for lack of water. 



B. Then water it freely and record the time required for the 

 leaves to begin to recover their natural position and the 

 time to recover fully. The time needed for the leaves to 

 begin to resume their ordinary position is that consumed in 

 entering the roots (largely through the root hairs) and push- 

 ing upward through the stem until the water pressure in the 

 leaves is restored to its normal amount. Filling the leaf 

 cells fuller of water (increasing their turgor) has the same 

 effect on their firmness that inflating a football or a bicycle 

 tire does upon its firmness. 



Reference. Pfeffer 31, I. 



32. Examination of twigs for starch. Cut thin cross sections of twigs of 

 some common deciduous tree or shrub in its early winter condition, moisten 

 with iodine solution, and examine for starch with a moderately high power 

 of the microscope. Sketch the section with a pencil, coloring faintly the 

 starchy portions with blue ink, used with a mapping pen, and describe 

 exactly in what portions the starch is deposited. 



33. A typical tuber : the potato. Sketch the general outline of 

 a potato, showing the attachment to the stem from which it grew.^ 



A. Note the distribution of the " eyes." Are they opposite or 

 alternate ? Examine them closely with the magnifying glass 

 and then with the lowest power of the microscope. What 

 do they appear to be ? 



B. If the potato is a stem, it may branch ; look over a lot of 

 potatoes to try to find a branching specimen. If such a one 

 is secured, sketch it. 



1 Hydrangea Hortensia. 



2 Examination of a lot of potatoes will usually discover specimens with an 

 inch or more of attached stem. 



