234 



Methods in Plant Histology 



and Delafield's haematoxylin. With any of these combinations, a 

 slight touch of orange usually adds to the beauty of the preparation. 

 This particular stem affords a fine illustration of the polystele. 

 Each bundle of the polystele has the form of a mesarch protostele. 

 In Osmunda, and in many other ferns of similar habit, the 

 rhizome is surrounded by the very hard leaf bases. Good sections 



FIG. 77. Pteris aquilina: photomicrograph of portion of one of the large bundles 

 in the rhizome; cut freehand and stained in safranin and Delafleld's haematoxylin. 

 X187. 



of the central cylinder can be secured only by dissecting away these 

 hard leaf bases and any hard portions of the cortex before attempting 

 to cut sections. A short distance back of the growing point will be 

 found a region which will show practically all the structures of the 

 mature stem, which will be easy to cut. Even in this region the leaf 

 bases should be dissected away. From the apical cell back to the 

 region where the sclerenchyma is beginning to turn brown, the ma- 



