1902.] KRAEMER— CONTIXUITV OF PROTOPLASM. 177 



ently toward iodine; the one rich in crystalloidal substance 

 becomes blue with iodine, whereas the other is not affected by this 

 reagent. 



In the studies of the author on the structure of the cell wall, the 

 following observations tending to show an analogy to the starch 

 grain have been made : 



(i) A similar layering of the cell wall, known as stratification 

 and striation, is readily observable in the walls of endosperm cells 

 as well as those cells impregnated more or less with mucilage, 

 lignin, cutin, suberin and allied substances. In some cases the use 

 of reagents, as acids and alkalies, may be necessary to bring out 

 this structure (Fig. 8). While it is not always easy to determine 

 the nature of the successive layers in the wall, still the structure 

 seems to correspond in the main to that of the starch grain, the 

 middle lamella of the cell corresponding to the point of growth. 



(2) The same kind of reagents, but in stronger solutions, may 

 be used to bring out the crystalline or spherite structure in the walls 

 of thickened parenchyma cells, as endosperm (Plate XXII, Figs. 9 

 and 13), or lignified cells, as stone cells. In cases where the cell 

 wall has been metamorphosed into mucilage, simple treatment with 

 water, as has also been shown to be the case with the starch grain, 

 is sufficient to bring out this structure. 



(3) The differentiation of the layers of the cell wall by the use 

 of aniline stains,* has not as yet been attended with any marked 

 degree of success. The use of swelling reagents, as sulphuric 

 acid, in conjunction with a stain, has, however, produced more or 

 less interrupted striae resembling the clefts and fissures in the starch 



* The methods involving the use of aniline stains in the study of the cell 

 wall are the same as those used in the study of the continuity of protoplasm, and 

 embody the three operations of fixing, swelling and staining, between each of 

 which operations the sections are washed quickly and with large quantities of 

 water. Fixing is usually accomplished by the use of aqueous iodine solutions 

 (.5 per cent, of iodine and .5 to i per cent, of potassium iodide); alcohol, osmic 

 and picric acids may also be employed. The swelling of the specimens is effected 

 by the use of dilute sulphuric acid (25 to 75 per cent.), iodine being sometimes 

 added to the sulphuric acid solution ; chlor-zinc-iodide and solutions of the alka- 

 lies are also employed for this purpose. The stains mostly employed are 5 per 

 cent, aqueous solutions of gentian violet, eosin or safranin, these being used in 

 connection with the swelling agents mentioned above. The time required for 

 each operation is usually from five to ten minutes, but when chloi -zinc-iodide is 

 used twelve hours may be required for the swelling. 



PROG. AMER. PHILOS. 800. XLI. 169. L. PRINTED JULY 28, 1903. 



