130 PLANT PHYSIOLOGY 



laboratory study (b) after paragraph 146). Keep in the dark 

 until the stem and roots are both in a vertical position. Place 

 in a box, closed on all sides, except for an opening about 10 

 mm. wide at one side, and direct this opening toward a win- 

 dow. Note the direction of curvature of stem and roots, as 

 well as the region where the curvature occurs. 



(/) Perform experiments similar to the foregoing, placing 

 orange-red glass or deep blue glass in front of the opening, and 

 note the results. 



(g) Sterilize some fresh horse manure in a steam sterihzer 

 to destroy all the fungi, and inoculate with the manure mold, 

 Pilobolus. When the sporangia of this are about to be formed, 

 place the dish containing the culture, micovered, in a dark box, 

 tilting the dish at an angle of 45 degrees toward one side, where 

 a small window about 2.5 cm. in diameter is left open to admit 

 light, but covered on the inside with a glass plate. Place the 

 box in such a position that the Hght can enter the window. The 

 sporangia will direct themselves toward the light and discharge 

 their spore masses, which will stick to the glass covering the 

 window. Only a few shots will fail to hit the ''bull's eye" 

 if the distance from the dish of the fungus to the window is 

 not more than 10 to 20 cm., although these are discharged with 

 considerable accuracy much further than that. Try the effect 

 of different colored glass on the accuracy of the aim. 



(h) Germinate a number of seeds of 

 broom-corn millet or proso {Panicum 

 miliaceum) in the dark, in a pot of earth. 

 When they have attained a length of 1 to 

 2 cm., cap the tips of half of the seed- 

 lings with httle caps of tinfoil, made over 

 the point of a pencil, and then gently 

 Fig. o5.-Phototropi3m ^lippcd ovcr the tip of the sccdling and 

 experiment {h). pinchcd in placc. Set the pot in the 



box used for experiment (e), and note the 

 result. Almost as good results can be obtained by using oats. 

 {i) Germinate seeds of bean, sunflower, mustard, etc. After 

 the seedlings show well-developed cotyledons, fasten several of 

 them by their middles in a horizontal position, under a bell-jar 

 over water, so as to keep the air moist and prevent the seeds 

 from drying out. Keep in a dark place for a few hours and note 

 the results. 



