THE MOLECULAR FORCES IN PLANTS. 



117 



protoplasmic construction to those of Elodea (see Fig. 38), as may 

 readily be determined if we remove with the forceps a tuft of 

 hairs from opening flowers of Tradescantia virginica, or a related 

 species, and examine them under the microscope. 



The now well-established fact that the protoplasmic masses of 

 neighbouring cells are almost universally connected with each 

 other by delicate plasmic threads travers- 

 ing the cell-walls, 1 is of the utmost im- 

 portance. 



We employ for investigation stems of 

 Rhamnus Frangula, at least 1 cm. in 

 thickness. These, after Strasburger, are 

 treated as follows : We remove the peri- 

 derm, and prepare very delicate tangential 

 longitudinal sections of the green cortex. 

 In examining the structure of the 

 secondary cortex, we direct our attention 

 particularly to the chlorophyll-containing 

 bast parenchyma, whose walls are pro- 

 vided with unbordered pits. The elements 

 of this bast parenchyma are rectangular 

 in form. In addition we see the elongated 

 bast fibres, and the spindle-shaped sections 

 of the medullary rays. We now bring 

 fresh sections from the secondary cortex 

 on to a cover-glass, add a drop of con- 

 centrated Sulphuric acid, and after a few seconds dip the cover- 

 glass into a vessel of fresh water, so as to wash the sections 

 rapidly and as completely as possible. We then stain the sections 

 with aqueous solution of aniline blue, wash with water, and mount 

 in glycerine diluted with water. Instead of aniline blue, we may 

 employ with advantage picric-aniline blue, prepared by dissolving 

 Picric acid to saturation in 5 per cent, alcohol, and adding aniline 

 blue till the fluid is bluish-green in colour. In successful prepara- 

 tions the walls of the bast parenchyma cells are so much swollen 

 that they have about the same diameter as the contracted and 

 stained plasmic cell contents, and the middle lamellae are also much 

 swollen. Not all preparations, and not all the cells of a prepara- 

 tion, are suitable for examination. The cells must be completely 

 intact, and the fixation by means of Sulphuric acid must have 

 been effected sufficiently quickly. 



Fio. 38. A cell of a staminai 

 hair of Tradescantia virgiriical 

 Magn. 240. (After Stras- 

 burger.) 



