THE DEVELOPMENT OF SOME SPECIES OF AGARICS 22/ 
epinasty continues to have its influence on the thin younger margin 
which is incurved or involute. 
Structure of the Stipe. — At the appearance of the pileus fundament, 
the stipe primordium is clearly differentiated as a definite region. 
At this stage the apparently homogeneous structure of the stipe pri- 
mordium is changed by the loosening up of its texture. There are 
strands of tissue running longitudinally through the stipe. These 
strands stain very deeply, causing them to stand out conspicuously. 
They intertwine with others in anastomosing fashion, thus forming 
intervening hyphal spaces. 
The stipe elongates by the lengthening of the cells. These ele- 
ments, in the stage of development represented by Figure 40, measure 
3-30/i in length. The increase in width is the result of branching and 
interstitial growth of the hyphae, and also by the increase in diameter 
of the cells themselves, which average 3.5 to 4)U. In more mature 
plants increased thickness is chiefly the result of the latter, as Hoffmann 
(14) on page 394 suggested. 
Hymejtophore Primordium. — The organization of the hymenophore 
primordium occurs simultaneously with that of the origin of the pileus 
margin. Like it, too, the development is centrifugal. The first 
differentiation of this tissue is in the angle between the pileus margin 
and stipe and on the upper surface of the stem. Because of the active 
increase in its elements and their richness in protoplasm the young 
hymenophore primordium takes a dense stain. 
As the pileus increases in width, its marginal hyphae add to this 
annular zone so that its surface is increased radially and upward 
(Fig. 43). Its elements multiply by intercalary growth and present a 
frazzled appearance, as observed in Coprinus comatus (5), Agaricus 
rodmani (4), and some other plants. 
Palisade Layer, Origin and Development of the Lamellae. — By con- 
tinued branching of the hyphae, the zone of primordial elements 
organize a definite layer of parallel threads which becomes more or 
less even on the surface since the ends of the hyphae reach the same 
level. This results in forming a compact layer of parallel threads 
perpendicular to the surface. Figure 44, is a transection through the 
upper part of the stipe and shows a portion of this structure immedi- 
ately beneath the curved pileus margin. The hyphal elements of 
this layer are slender, cylindrical, septate threads, 4.5-6/1 in diameter 
and 35/x in length. The terminal cell is longer than the others of the 
