and Laboratory Methods. 2515 



Methods in Plant Physiology. 

 XV. 



RESPONSE TO CHANGES OF TEMPERATURE. 

 Select a tulip which is ready to open, or has very recently opened, and 

 fasten it in a test tube or a small bottle of water by passing the stem through a 

 hole in the cork. If the tulip is closed, place it in a temperature of '10° to ■i7°C. 

 When it is well opened, transfer it to a temperature of 8° to 1'2° C. The change 

 from warm to cold and from cold to warm temperature may be made several 

 times, the temperature and the time being noted for each response. 



RESPONSE TO CONTACT STIMULUS. 



1. Experiments with Blossoms of Berberis vulgaris. Explore with a bristle the 

 blossoms of the barberry (^Berberis vulgaris) growing in the open to determine in 

 what stage of development of the flower the stamens are irritable. When this 

 has been determined, pick and place in a damp chamber several clusters of 

 blossoms and carry them to the laboratory. 



While the flowers are still in the damp chamber, explore all the organs with a 

 bristle to determine which ones and what parts are sensitive, dissecting off any 

 organs that may interfere with the search. After dissecting off any members 

 the blossom should be allowed to remain at rest for ten or fifteen minutes to 

 recover from the shock. 



When the sensitive area has been carefully localized determine : 



((?) The latent period at room temperature, recording the temperature ard 

 having the water containing the blossoms at the exact room temperature. 



{b) The latent period at 8° C. 



(r) The time, at a given temperature, required for the return of an organ to its 

 original position. 



{d') The number of times, at a given temperature, an organ will respond 

 to successive stimulation. 



{e) The effect of an induced electric current. For this test the flower stalk 

 should be fastened to one wire, and the other wire brought into contact with 

 various parts of the blossom. 



(y) The effect of an anesthetic on the irritability. To carry out this test a 

 few flowers are to be floated on water in three or four watch crystals, and one or 

 more stamens of each tested for irritability. The blossoms that are found irri- 

 table are then to be placed, while still in the watch crystals, under a bell-jar having 

 a capacity of 1 or '1 liters. At the same time a watch crystal containing about 

 1 c. c. of chloroform is introduced under the bell-jar. After five minutes have 

 elapsed, the bell-jar is raised enough to allow the removal of one watch crystal 

 and the sensitiveness of the stamens is tested. At the end of another period of 

 five minutes another watch crystal is removed and the flowers tested, and so on 

 until the stamens no longer respond to contact. Such insensitive blossoms are 

 then allowed to stand in the open air and are tested at intervals of five minutes 

 for the return of sensitiveness. 



