432 Plant Physiology 



LABORATORY WORK 



Orientation. Make and record observations in the open or 

 in the greenhouse upon the relations of shoots and leaves of 

 any plant to light. Begonia, grape, or Norway maple may be 

 used ; also note the relations of the compass plant (Lactuca 

 Scariola) if available. 



Place a pot or water culture containing seedlings (several 

 centimeters high) in a chamber permitting one-sided illumina- 

 tion. The chamber may consist of a tight box, black on the 

 inside, arranged with a slit on one side through which rays of 

 light may be admitted. Place the plants as far as possible 

 from the source of light, and for some hours note the response 

 of the shoot (and also of the root if a water culture is employed). 

 Expose another plant which has been in complete darkness to 

 one-sided illumination for some moments and then return it to 

 a dark chamber. Note any subsequent response and discuss 

 the results. 



Light perception. Make hand sections of leaves of oats, 

 hyacinth, hepatica, Saxifraga Geum, or Garry a elliptica, and 

 describe the lens-shaped cells or epidermal modifications con- 

 sidered by Haberlandt and some others to be light-perceptive 

 organs. Consult the article cited by Wager, note his method 

 of photographing objects through cells, and read his conclusions 

 regarding light perception. 



Wave length and rate of growth. With bottles, test-tubes, 

 and corks prepare three pieces of apparatus as shown in Fig. 

 122. Prepare the solutions of (1) ammoniacal copper carbonate 

 and (2) naphthol yellow, so as to give practically pure colored 

 lights (spectroscopically tested, if possible), the one excluding 

 practically all except blue and blue violet rays, and the other 

 excluding all except the red end of the spectrum. Fill one 

 bottle three fourths full with each of these solutions and one 

 with water. Place in each test-tube, on filter paper or moss, a 

 germinated seed of the field pea, and insert the tubes as shown 

 in the figure. Relative growth may be observed until the seed 

 have outgrown the chambers. With the apparatus commonly 



