146 ILLINOIS ACADEMY OE SCIENCE. 



results, but led to experiments with normal green leaves in which 

 the veins and veinlets appear white when seen by transmitted 

 light. Positive results have been obtained with leaves of bean, 

 corn, barley, turnip, lettuce, Easter lily, Chinese sacred lily, 

 freesia, and lilac. Leaves of corn and barley grown in the labo- 

 ratory are preferred for use by students in simple demonstrations 

 and also for projection experiments. For study under the com- 

 pound microscope leaves of the bean and lilac are preferred. 



The rate of movement in the veins varies greatly, but, in gen- 

 eral, appears to be more rapid than has been observed in stems. 

 I have repeatedly noted a rate of 30 mm. in fifteen seconds, but 

 the maximum rate observed by my students seems to be consid- 

 erably faster. These measurements were made by direct observa- 

 tion. For observing the phenomenon as it is related to the lumen 

 and walls of the tracheae it is necessary to use the compound 

 microscope with a power as high, at least, as a quarter inch 

 objective and one inch ocular. It is possible to identify the 

 tracheae in the smaller xylem strands and note the normal con- 

 ditions of the lumen and wall and a moment later observe the 

 movement of the colored liquid through the lumen of the cell. 



Troublesome conditions are met with in the manipulation of 

 the leaves under the compound and projection microscopes. 

 New forms of apparatus, devised by the author, for the control 

 of these conditions are not yet sufficiently perfected for publica- 

 tion but will be included in a report of further researches. 



The laboratory demonstration included, first, the methods of 

 preparation of the leaves for direct observation with the eye 

 alone or aided by a hand magnifier and, second, the exhibition 

 and description of a special cell for use in projecting the moving 

 stream, the method of mounting a leaf in this cell and the dem- 

 onstration of the movement by projection on a screen. 



The first method, as used by students in the biological labora- 

 tory of the Chicago Teachers' College was worked out and the 

 specimens passed to members of the Academy. The leaves used 

 were from barley plants from six to ten inches high, grown in 

 the biological laboratory of the college. A few drops of a strong 

 aqueous solution of eosin were placed in either a small homeo- 

 pathic vial or in a watch glass. A leaf was cut, with a sharp 

 knife, at a right angle to its length and at a half inch or more 

 from its attachment to the stem. The cut end was immediately 

 placed in the solution of eosin and the specimen held between 



