142 TROPISMS 



the axis of the body of the spermatozoa toward the capil- 

 lary tube containing malates or succinates, as the tropism 

 theory demands. 



When the capillary tube and the surrounding medium 

 contain the same solute for which the organisms are posi- 

 tively chemotropic, they will not go into the tube unless 

 the concentration in the tube is a definite multiple of the 

 concentration of the outside solution. Thus Pf effer found 

 that the concentration of sodium malate in the capillary 

 must be at least thirty times as great as in the outside solu- 

 tion to induce the spermatozoa of fern to move into it, and 

 in the case of Bacterium termo the solution of meat ex- 

 tract in the tube had to be at least four times as great as 

 the outside solution. In the case of Isoetes spermatozoa 

 Shibata found the ratio of about 400 to 1. This constancy 

 of the ratio is known as Weber's law, which therefore 

 holds for chemotropic phenomena. 



Lidforss 281 found with the aid of Pf effer 's method 

 that the spermatozoa of Marchantia are positively chemo- 

 tropic to certain proteins, especially egg albumin, vitellin 

 from the egg yolk, hemoglobin, and mucin of the sub- 

 maxillary gland; blood albumin, casein, and legumin were 

 less effective. The lowest concentration for hemoglobin 

 solutions and for egg albumin was 0.001 per cent. ! 



It may also be stated that Lidforss found a chemo- 

 tropic effect of proteins upon the direction of growth of 

 pollen tubes. 280 



Bruchmann 81 found that the spermatozoa of Ly co- 

 podium were positively chemotropic to the watery extract 

 in which pieces of the prothallium had been boiled. Pfef- 

 fer's capillary method was used. They showed also posi- 

 tive chemotropism to tho citrate anion. Thus, sodium 

 citrate was pfficient in a 0.1 to 0.5 per cent, solution. TJip 



