280 HISTOLOGY OF MEDICINAL PLANTS 
nently papillate. The under epidermis consists of wavy cells 
without papilla. Another view of the papilla is shown in 
Fig. 6. The parenchyma of the ray flowers (Fig. 7) contain 
cubical crystals. The lobe of the disk-flower petal (Fig. 8) 
is papillate at the end, the terminal cells have thick outer and 
thin inner walls. The filament tissue (Fig. 9) is composed of 
nearly square cells. The calyx tissue (Fig. 10) is made up of 
thin-walled cells with slightly papillate margins. The lobe of the 
stamen (Fig. 11) consists of nearly uniform epidermal cells 
which are in contact throughout their long diameter, while the 
hypodermal cells are thin-walled and angled. The pollen grains 
(Fig. 12) are dark yellowish green, thin, and the wall does not 
appear perforated by pores. The papille of the stigma (Fig. 13) 
are clustered, club-shaped, and nearly white in color. They 
are usually found detached in the powder. All parts of the 
pistil contain secreting cells, but the most conspicuous secreting 
cavities (Fig. 14) are those of the ovary. These cavities appear 
brownish in color and are surrounded by small cells which appear 
indistinct on account of the great number of superimposed cells. 
The parenchyma of the receptacle occurs in fragments which 
have strongly marked porous walls. 
OPEN INSECT FLOWERS 
Many of the structures of open insect flowers (Plate 119) 
are similar to those found in the closed flower. There is prac- 
tically no difference in the edge of the scale (Fig. 1); or the 
fibre of the scale (Fig. 2); or the T-shaped hairs (Fig. 3); or the 
upper epidermis of the ray flower (Fig. 4); or the under epidermis. 
of the ray flower (Fig. 5); or the cross-section of the ray petal - 
(Fig. 6); or the lobe of the disk petal (Fig. 7); or the filament 
tissue (Fig. 8); or the lobe of the stamen (Fig. 9); or the papilla 
of the stigma (Fig. 12); or the parenchyma of the receptacle 
(Fig. 15). The difference in structure is found, first, in the 
involucre scales, which are more fibrous than the scales of the 
closed flowers; secondly, in the pollen (Fig. 11), which is less 
abundant than in the closed flower; it is also lighter in color 
and usually shows the wall perforated by three pores; thirdly, 
the outer layers of the achene consist of thick, porous-walled 
stone cells (Fig. 13), which occur singly or in groups; fourthly, 
