60 INFLUENCE OF CHEMICALS 



antherozoids will have escaped and be moving rapidly around in 

 the liquid. Remove the capillary tube one minute later, and ex- 

 amine under the microscope for antherozoids. 1 Make a second 

 test and allow the capillary tube to remain in the water with the 

 motile bodies for five minutes. Compare the number of the 

 antherozoids which have entered the tube with that of the first 

 test. The archegonial cells contain salts of malic acid, and these 

 substances serves to attract the swimming antherozoids, and thus 

 secure fertilization of the egg-cells. 2 Hairs of Heracleum contain- 

 ing malic acid may be used instead of the glass tubes. 



95. Chemotactic Movements of Bacteria. The stimulating 

 power of food substances may be seen if the movements of bac- 

 teria are studied. Boil a pea or two for a few minutes, then put 

 it in a few cc. of water in an open dish and allow it to stand for 

 a day or two. Spores of Bacterium termo floating in the air will 

 have fallen into the liquid and developed great numbers of colonies 

 and individuals. Filter some of the liquor containing the bacteria 

 through glass wool to obtain a solution in which individual bac- 

 teria are swarming. Now place a large drop of the culture on a 

 glass slip. Prepare capillary tubes as in the previous experiment, 

 but fill them with a one-per-cent. solution of extract of beef (com- 

 mercial preparation). Thrust the ends of one or two of these 

 tubes in the bacterium culture drop for a few minutes. Examine 

 with a microscope and note the number of the organisms that 

 have been attracted to the beef solution and entered the tube. 



96. Chemotropic Movements of Pollen Tubes. The demonstra- 

 tions with bacteria and antherozoids showed that these bodies 

 actually move toward a spot in which the stimulating compound 

 is found in an optimum intensity. In certain instances the plant 

 structure does not move, but directs its growing parts toward the 

 optimum intensity of the stimulating agent. Add i g. of gelatine 



1 Pfeffer. Locomotorische Richtungsbewegungen durch chemische Reize. Unter- 

 such. a. d. Bot. z. Tubingen. I : 363. 1884. 



2 Buller, A. H. Contributions to our knowledge of the physiology of the sperma- 

 tozoa of ferns. Annals of Botany, 14 : 543. 1900. 



