280 HISTOLOGY OF MEDICINAL PLANTS 



nently papillate. The under epidermis consists of wavy cells 

 without papillae. Another view of the papillae 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. n) 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 papillae 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. i); 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 papillae 

 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. n), 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, 



