METHODS. 



27 



Tradescantia zebrina. — Large mechanically sensitive stomata; stomata at edge of piece 

 flooded by running absolute alcohol under the cover, and constantly watched. 



That the preservation of the form of the stomata is due to the rapid extrac- 

 tion of the water is shown by the fact that, if a piece of epidermis is fixed in 

 alcohol and then mounted for examination in the same fluid, the opening may 

 be made to close by the addition of water. 



The movement will take place just as in life, so that one who is not aware 

 of the conditions will at once suppose that the closure is due to plasmolysis. 

 This of course has really occurred in the dead tissue ; what happens now is 

 merely the restoration of the water to the walls, this being accompanied by 

 the return of the elastic condition. The change occurs, therefore, because 

 the shut condition is the normal one when the turgor of the cell is low. 



Table 16. — Transverse measurements, Tradescantia zebrina. 



First { In water 



\ In absolute alcohol 



c , < In water 



Second - ( In absolute a i co hol .... 



Measurements made of outer and inner 

 openings, by appropriate focusing:* 



Outer in water 



Outer in absolute alcohol 



Inner in water 



Inner in absolute alcohol 



Specimen passed through — 



Absolute alcohol 



Clove oil 



Xylol balsam 



* Plate 4, figs. 4 and 5. 



The application of the absolute alcohol method to other plants must be 

 made with due caution. I have recently tried it with Brodiosa, with some 

 degree of uncertainty. I found that when the epidermis is stripped and exam- 

 ined in water the stomata expand. Upon being placed in absolute alcohol 

 the epidermis, which is made up of long, slender cells, shrinks longitudinally 

 and apparently presses the stomata in this direction, so that the pores become 

 distorted. When the epidermis is placed in the alcohol immediately upon 

 stripping the stomata are preserved nearly as in normal condition. 



Most beautiful preparations may be made by the above means. Thus, the 

 fine large stomata of our cultivated Zebrina, usually referred to as Trades- 

 cantia zebrina, may be preserved in any condition. The illustrations in plate 

 4 from photomicrographs made from my own preparations bear sufficient 

 evidence of the results. 



