44 
GERTRUDE E. DOUGLAS 
contact having grown together (fig. 59). The trama of the gills has a 
very loose mesh which brings into sharp relief the deeply stained, 
crowded palisade layer, which covers the surface of the gills (fig. 59). 
In figure 66, an enlargement of the section shown in figure 61, the 
very uneven character of the palisade layer on the edge of the gills is 
apparent. The triangular form of the gill in section appears in the 
nearly mature plant of figures 64 and 65. The tissue of this fruit body 
is still homogeneous in character, except for the gills and the slime- 
producing layer over the surface. The portion of the pileus at this 
time is beginning to take on a hyponastic growth, causing the mush- 
room to become umbilicate. 
Hygrophorus borealis Pk. 
(Figs. 67-80) 
Early Stages.- — ^The development of this species resembles that of 
H. miniatus and H. nitidus so closely that it will not be necessary to 
enter into its life history with as much detail. The youngest button 
found was nearly oval in shape and entirely homogeneous in com- 
position (fig. 67). For a time after this the fruit bodies elongate very 
rapidly (figs. 68, 69), growing chiefly at the apex, as shown by the 
deeper stain in this region. At length, when they are well up out of 
the soil, the hyphal elements in the apex multiply and turn outwards 
in epinastic growth. Thus the pileus is formed (figs. 70 and 71). 
At practically the same time, the hymenophore primordium becom.es 
organized (figs. 70, 71 and 72) in the annular constriction between 
the fundaments of pileus and stem. A very strong epinastic growth 
causes the margin of the pileus not only to bend downward but to 
inroll. Thus a protection is obtained for the young gill salients as 
they form. Before their appearance, however, a definite, even palisade 
layer is formed (figs. 73, 74 and 75). 
Development of Gills. — Unfortunately very early stages in the 
formation of the gills are lacking. Figures 76-80 represent the young- 
est stage found. It corresponds very nearly to the stage represented 
in figures 36-39 in H. miniatus and shows the progressive maturity 
of the young ridges, as one passes from the margin (fig. 80) inward to 
the center (fig. 76). In figure 80 the dark stain represents the hymeno- 
phore primordium seen in surface view on the inside of the inrolled 
margin of the pileus. Figure 81 represents a very nearly mature 
