2428 Journal of Applied Microscopy 



The potato inoculated with dirt from the surface of a potato will show colo- 

 nies with a wrinkled surface, the so-called potato bacillus. The preparation 

 from these colonies will show rod shaped organisms. In some of the cells may 

 be seen bright bodies which are not stained (Fig. 17). These are spores, the 

 stage of the organism which renders many bacteria so resistant to heat, drying, 

 and disinfectants. Note the size of the spores, whether of a greater diameter 

 than the cell or not, and the position in the cell. W. D. Frost, 



University of Wisconsin. E. G. HASTINGS. 



Methods in Plant Physiology. 

 XIII. 



HELIOTROPISM— Continued. 



10. Diaheliotropism, or Transverse Heliotropism. — The movements studied 

 under this head are those reactions by which a plant or plant-organ is placed at 

 right angles to the rays of light; in any other position it is out of equilibrium. 

 The best examples are to be found in leaves. Observe plants with both fixed 

 and motile diaheliotropic leaves, noting in each case how the diaheliotropic 

 position is attained. 



11. Positions Due to Specific Sensitiveness. — Find out of doors a young dande- 

 lion {laraxacum officinale) or thistle {Cnicus laficeolatus) with leaves closely 

 appressed to the ground. Carefully remove the earth beneath the leaves with a 

 knife and observe whether the leaves change their position. Determine whether 

 the change of position is forcible or passive. 



Dig up a similar plant with a large ball of earth, place it in a pot and set it 

 in a dark chamber. After 24 to 48 hours observe the change in the position of 

 the leaves. When the leaves are about 45° above the horizontal, fasten it to the 

 klinostat and revolve it before the window. The axis of the klinostat should 

 point toward the window and the axis of the plant should be parallel to the axis 

 of the klinostat. In two or three days the leaves will have curved away from 

 the light and their laminae will be approximately at right angles to the direction 

 of the incident rays. 



Revolve another plant on the same klinostat with its axis at right angles to 

 the axis of the klinostat and at right angles to the light rays. The leaves point- 

 ing towards the light curve downwards, while those pointing away from the light 

 curve upwards, until the laminae of both are at right angles to the incident light. 



As a result of these observations determine what stimuli are shown to be 

 active in determining the position of these leaves. 



12. Comparative Intensity of Response to Light and to Gravitation. — Select two 

 crocks of mustard {^Sinapis albd) or radish (^Raphanus sathnis) seedlings with 

 erect stems 3 to 5 cm. high and place them in a heliotropic chamber with an open- 

 ing which admits light at the level of the seedlings. Lay one crock on its side 

 with the stems pomting horizontally toward the light, and set the other crock 



