VIII Journal of Agricultural Research voi. xvi 



Effect of Certain Compounds of Barium and Strontium on the 

 Growth of Plants 



Page. 

 Plate 24. A. — Effect of barium on the growth of cowpeas with and without 

 calcium carbonate. B. — Stimulating effect of barium on root growth of 

 cowpeas. C. — Effect of barium on the growth of soybeans 194 



Angular-Leafspot of Tobacco, an Undescribed Bacterial Disease 



Plate 25. A. — A tobacco leaf showing an early stage of the angular-leafspot. 



B. — Angular leaf spots on a tobacco leaf 228 



Plate 26. A. — Upper surface of a tobacco leaf affected with the angular- 

 leafspot. B. — Lower siirface of a tobacco leaf affected with the angular- 

 leafspot 228 



Plate 27. A. — Angular leaf spots on a tobacco leaf as seen in transmitted light. 



B. — ^Atypical angular leaf spots on a narrow leaf of tobacco 228 



Two Species of Pegomyla Mining the Leaves of Dock 



Plate 28. A. — Eggs of Pegomyia affinis. B. — Parasitized eggs of Pegomyia 

 calyptrata. C. — Eggs of Pegomyia calyptrata. D. — A small mine on Rumex 

 leaf, showing the original linear mine and the beginning of the blotch mine. 

 E. — Atypical mine on Rumex oblusifolius produced by the larva of Pego- 

 myia calyptrata. F. — A monstrosity, an adult P. calyptrata issuing feet first 

 from its puparium. G. — A typical mine on Rumex crispus produced by 

 the larva of Pegomyia calyptrata. H. — A mine on Rumex obtrusif alius, pro- 

 duced by a nearly mature larva entering a new leaf to complete its develop- 

 ment 244 



Plate 29. A. — Fiske cages, used in studying the adult flies of Pegomyia spp., 

 showing the arrangement in outdoor insectary. B. — Glass cylinder cage, 

 used in studying habits of adult flies. C. — Fiske cage, used in studying 

 habits of adult flies 244 



Plate 30. A. — Ventral aspect of posterior segment of larva of Pegomyia affinis, 

 showing lobes and anal opening. B. — Lateral aspect of posterior segment 

 of larva of P. affinis, showing tubercles. C. — Lateral aspect of posterior seg- 

 ment of larva of P. calyptrata. D. — Ventral aspect of posterior segment of 

 larva of P. calyptrata, showing lobes and anal opening. E. — " Pseudo- 

 cephalon" (Henneguy) of P. calyptrata: a, buttonlike areas referred to 

 in text; 6, sensory papilla; c, antenna; d, mandibular sclerite; e, anterior 

 spiracle. F. — Posterior spiracle of larva of P. calyptrata 244 



Influence of Foreign Pollen on the Development of VANaLA Fruits 



Plate 31. A. — Left to right. Vanilla planifolia, first of each pair close-fertil- 

 ized, second fertilized with- vanillon pollen. B. — Cross sections of same 

 fruits 353 



Pate 32. A. — Vanillon No. 13 fruits, close- and cross-fertilized. Lower row 

 close-fertilized, upper fertilized with pollen of Vanilla planifolia. B. — 

 Cross section of same fruits 252 



Plate 33. A. — Vanillon No. 34: Fruits at right fertilized with pollen of 



Vanilla planifolia, left close-fertilized. B. — Cross sections of same fruits. 252 



Plate 34. A. — Vanillon No. 43 fruits. Upper row fertilized with pollen of 

 Vanilla planifolia, lower row close-fertilized. B. — Cross sections of same 

 fruits 252 



