124 



Elementary Plant Physiology. 



tions, and note differences in structure. It would also be of 

 interest to cultivate some of these plants in an aquarium, 

 and observe the manner of formation of the leaves on sub- 

 merged and on aerial portions 

 of the same stem. 



136. Ch em o t r o pic 

 movements of pollen 

 tubes Add i gram of gela- 

 tine and 4 or 5 grams sugar 

 to 50 cc. distilled water. 

 Warm until all are dis- 

 solved together. Place a drop 

 of the solution on a glass 

 slip, and add a number of 

 pollen grains of Narcissus, 

 Litium, Fritillaria, or Lathy- 

 rus. Cover with a thin circle 

 of glass, such as is used in 

 mounting objects for the mi- 

 croscope, and keep in a room 

 at about 18 C. for eight or ten 

 hours. Examine with mag- 

 nifications of 60 and 400 

 on the following day. Note 

 the germination of the pol- 

 len cells, and also the direc- 

 tion which the tubes have 

 taken. All seem to be di- 

 rected away from the edge of 

 the cover glass. It would be 

 profitable to make a second 

 Fig. 97 . Positions assumed by preparation and keep it with 



leaves of Mimosa in response to fa Q fi rstj care f u lly sealing the 

 stimulus applied to tip of leaflet on . . , 



right< edges of the preparation with 



