A STUDY OF DEVELOPMENT IN THE GENUS CORTINARIUS 323 
appearance shown in figures 3 and 10, and in the tangential section 
of the same fruit body (fig. 4). Soon, however, as new elements are 
formed in a centrifugal manner, the zone of the hymenophore near 
the stem begins to change its appearance. The ends of the hyphae 
become more even and stouter, thus forming the dense palisade tissue 
shown in figures 5, 6, and 7, and in the slightly older fruit body of 
figures 8, 9, and 11. It is in this stage that we first find evidence of a 
gill cavity. The palisade layer becomes very crowded on account of 
the broadening of the hyphae and the interpolation of new elements. 
At the same time the growth of the pileus becomes strongly epinastic. 
These two factors together exert considerable tension on the hyphae 
of the ground tissue, with the result that they finally break and leave 
a cavity below the palisade layer. The ragged under surface of the 
latter in these figures is due to the ends of the broken hyphae. Many 
seem to be able to stand considerable stretching, so that the cavity at 
first is rather weak. It is, however, important to notice that before 
there is any evidence of gill formation, there is a well defined, even, 
palisade layer. 
Origin of the Partial Veil. — ^We have seen that very early in the 
life history of the fruit body, the pileus and stem primordia are differ- 
entiated by the appearance of a dome-shaped area, growing very 
actively at its margin and here forming the primordium of the hymeno- 
phore. The general region of looser plectenchyma, extending over 
the pileus, outside the hymenophore and down over the stem primor- 
dium, is the blematogen. The ground tissue within this somewhat 
indefinite zone, lying between the margin of the pileus and the stem 
fundaments, represents, as before noted, the partial veil. As the 
plant matures, the upper part of the pileus fundament grows into and 
becomes consolidated with the blematogen, which forms here a firm 
cortex. At the sides, however, the blematogen shows a more or less 
duplex character (figs. 3 and 5). There is a very thin but firm outer 
layer, which stains very deeply and is composed of two or three rows 
of parallel or slightly interwoven hyphae with large diameters. With- 
in, the blematogen is very loose and delicate and is exactly similar to 
the tissue of the partial veil. This double character may be dis- 
tinguished even on the upper surface of the pileus margin (figs. 3, 5, 
and 8), where the outer layer merges into the cortex of the fruit body, 
quite similar in its composition. This rind is very persistent, retaining 
its integrity until after the gills are fairly developed (fig. 17). It is 
