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EXPLANATION OF PLATES. 



Plate I. — Spots produced by aphides and thrips. Figs. 1, 2, 3, and 4 show the 

 early, intermediate, and late stages of the disease produced by aphides, as seen when 

 examined by transmitted light. (Natural size.) Figs. 5, 6, 7, 8, and 9 show the 

 distortion of the leaves and the spots produced by thrips. (Natural size.) 



Plate II. ^Photomicrograph of sections to show early stages of stigmonose pro- 

 duced by aphid punctures. Fig. 1 shows a section of a healthy mature leaf. The 

 chloroplasts show as small dots lining the palisade parenchymal cells. There are 

 very few in the large water storage cells surrounding the vascular bundles in the 

 middle of the leaf. (X 30 diameters.) Figs. 2 and 3 show the sucking apparatus 

 of two aphides passing between the epidermal and mesophyll cells of a young leaf to 

 the soft bast of the vascular bundle. The aphides were killed on the surface of the 

 leaves and the section cut after dehydration and infiltration with paraffin. (Fig. 

 2 X 120 and fig. 3 X 70 diameters.) Fig. 4 shows the proteid sheath secreted by an 

 aphis while inserting its sucking apparatus in the tissues of a young leaf. A part of 

 another sheath is shown in the lower right-hand portion of the section, (x 200 

 diameters.) 



Plate III. — Photomicrograph of sections to show later stages of stigmonose pro- 

 duced by aphid punctures and thrips. Fig. 1 shows a cross section illustrating 

 enlargement of cells and loss of chloroplasts on both sides of the line of puncture, 

 (x 75 diameters.) Fig. 2 shows a more advanced stage, (x 65 diameters.) Fig. 3- 

 shows a cross section illustrating a late stage, many of the cells being broken down 

 and the cell contents in a number of instances forming globular plasmode structures. 

 (X 85 diameters.) Fig. 4 shows a spot produced by thrips. The epidermal cells 

 have collapsed completely and the cuticle has become disorganized, but still 

 remains. Most of the immediate vmderlying cells have lost their chloroplasts. 

 (X 85 diameters.) 



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