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ATKINSON— MORPHOLOGY AND 



[April 23, 



longitudinal section two such areas are seen, symmetrically situated 

 on either side of the long axis and some distance from the surface of 

 the fruit body. The annular zone is of quite limited extent as the 



2 3 



I 



2 3 



Diagram i Lateral view through young basidiocarp representing early 

 stage of differentiation into the primordia of the four principal parts ; pileus 

 area, stem area, hymenophore fundament (H3O and veil primordium (F. P.)- 



Diagram 2. Zenith view in young basidiocarp at same stage of 

 fundaments, and annular hymenophore primordium. See text for details. 



small area presented by its transection in Fig. 3 shows. The outline 

 of this area in transection is somewhat elongated and rises at an 

 oblique angle from the stem area, well shown in Fig. 3 and indi- 

 cated in diagram i. The area of the primordial hymenophore seen 

 in the tangential section is much more extensive as shown in Fig. 4. 

 The difference in the extent of these areas shown in median (Fig. 3) 

 and tangential (Fig. 4) sections is clearly appreciated by reference 

 to diagram 2. 



Structure of the Young Hymenophore Primordium. — This inter- 

 nal annular zone of new growth arises by the origin of numerous, 

 slender hyphal branches, rich in protoplasm, which are directed 

 downward, or obliquely downward and outward. They have a 

 more direct course than the hyphae of the basidiocarp primordium, 

 the latter irregularly sinuous and interwoven, while the hyphae of 

 the young hymenophore primordium are nearly or quite straight. 

 Because of their small diameter and their slender, gradually taper- 

 ing ends, they easily crowd their way through the rather open weft 

 of hyphae forming the ground tissue or fundamental plectenchyma. 

 Fig. 9 is a highly magnified view of the hymenophore primordium 



