308 



METHODS IN PLANT HISTOLOGY 



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The rhizome of Adiantum affords a good ilkistration of leaf gap and 

 leaf trace. The vascular cylinder is a mesarch siphonostele; but there 

 are few sections like Figure 96, because the cylinder is so interrupted 

 by leaf gaps. This rhizome cuts well without imbedding. The petiole 



of Botrychium, in transverse 

 sections below the fertile spike, 

 shows the interesting leaf-trace 

 situation which proves that 

 the fertile spike consists of a 

 pair of pinnae fused together.. 

 The ferns of the Gray's 

 Manual range afford no very 

 satisfactory material for illus- 

 trating the protostele, although 

 protosteles occur in Lygodium 

 and Trichomanes. The most 

 satisfactory material is Glei- 

 chenia, a very common and 

 very beautiful fern in tropical 

 and subtropical regions, but 

 almost never seen in green- 

 houses or even in botanical 

 gardens. Formalin-alcohol ma- 

 terial can be cut without im- 

 bedding and is easy to stain. 



The Gleichenia rhizome is 

 one of the most difficult of all 

 fern rhizomes to imbed in 

 paraffin and cut. The most 

 beautiful sections of this rhizome we have ever seen were cut in 

 paraffin by Dr. Fredda Reed. This is the method : 



1. Cut the rhizome into pieces 1 cm. long. 



2. Twenty per cent hydrofluoric acid, 3 or 4 days. 



3. Wash well in water. 



4. Dehydrate in 10, 20, 30, 40, 50, 70, 85, 95, and 100 per cent alcohol, 24 

 hours in each. 



5. One-fourth xylol, f absolute alcohol, 12 hours. 

 One-half xylol, | absolute alcohol, 12 hours. 



Fig. 98. — Osmunda cinnamomea: photomicro- 

 graph of single bundle of the mesarch siphonostele. 

 Stained in safranin and anihn blue. Eastman Com- 

 mercial Ortho film, Wratten C filter (blue-violet) ; 

 Bausch and Lomb 4-mm. objective, N.A. 0.65; 

 exposure, 4 seconds. Negative by Dr. P. J. Sedg- 

 wick. X108. 



Three-fourths xylol. 

 Pure xylol, 12 hours. 



absolute alcohol, 12 hours. 



