1894.] Comparative Histology of Pulvint. 491 
be in the center of the stele or it may be represented by the 
thickened cells at the hilum, which is always on the dorsal 
side of the organ. Generally speaking the elements of the 
steles are poorly developed. ~ 
8. The well developed organ always shows marked trans- 
verse folds even in the diurnal position, which become 
changed when the curvature of the organ becomes greater or 
less. Many organs show a compression and distortion of the 
cells in the region of the transverse folds. 
_ 9. Some organs must be regarded as enlarge 
ing to the old idea while others are distinctly contractions, 
The former is generally the case with primary organs and the 
latter more commonly with secondary and tertiary organs- 
Madison, Wis. 
ments accord- 
EXpLANATION OF PLaTe XXXIV. 
All figures except fig. 5 represent Melilotus alba. 
Fig. 1. Diurnal position of leaf turned towards the west. 
Fig. 2. Nocturnal position. ; ‘ 
Fig. 3. Epidermal and collenchyma cells from the cross sectio 
atl organ. 
ig. 4. Diagram of cross section of primary organ. 
Fig. 5. Trifolium repens. Ey podeciial parenchyma cells from motor organ. 
Longitudinal section. 
ig. 6. Cells from longitudinal section 0 
oe 7. Diagram of longitudinal section 0 
n of the pri- 
f secondary organ. : 
f secondary organ, nocturnal posi- 
ti 
Fig. 8. The same, diurnal position. 
Fig. 9. Diagram of cross section of petiole. 
Fig. to. Diagram of cross section of secondary organ. 
