VIII Journal of Agricultural Research voi. xix 



Page 



21. A. — A near view of the thick down of conidiophores which has been pro- 



duced on the upper stirface of a badly diseased maize leaf. B. — Upper 

 surface of a badly infected maize leaf from a maturing plant. C. — Upper 

 surface of the middle portion of a maize leaf from a very young plant 

 which has only recently developed the markings of the disease 122 



22. A. — View of a row of Egyptian sorghum showing tall, green, healthy plants 



at tlie left and at the right a dwarfed, yellowish white plant whitch is in- 

 fected by the downy mildew. B. — Near view of this diseased sorghum 

 plant. C. — A comparative view of healthy teosinte (right), and teosinte 

 seriously infected with the downy mildew (left) 122 



23. A. — Portion of the typical crooked, irregular mycelum with nximerous 



haustoria which is found in the mesophyll of badly infected leaves, here 

 freed from the host tissue by maceration. B.— Longitudinal section cut 

 from the center of a maize stem 8 inches from the ground. C. — Portion of 

 the mycelium freed by maceration from tissue of the midrib at the base 

 of a badly infected leaf. D. — Hypha cut in cross section as it lies be- 

 tween three adjacent mesophyll cells of the host. E. — Transverse sec- 

 tion from a badly infected portion of a maize leaf, sho-wing the abundant 

 mycelium running between the cells of the bundle sheath and forming 

 in the substomatal air chamber the branches (a) that grow out through 

 the stoma to form the conidiophores. F. — Portion of a hypha lying 

 between adjacent mesophyll cells, one of which has formed a many- 

 layered wall around the haustorium invading it. G. — Portion of a 

 hypha similar to that shown in F but with the haustorium unhindered 

 in its invasion of the host cell. H. — Bit of mycelium such as is shown 

 in A but more highly magnified to show the haustoria 122 



24. A. — Slender, sparingly branched conidiophore bearing comparatively few 



conidia. B. — Tip of branch with two conidia in situ. C. — Stout, much- 

 branched, mature conidiophore bearing 38 spores. D. — Upper portion 

 of a nearly mature conidiophore with one secondary branch which has 

 failed to branch further and has terminated in a single conidium only. 

 E. — Small, stunted, sparingly branched conidiophore produced on 

 maize during the light dew of the hot, dry season. F. — Basal cell with 

 two thick crosswalls; from maize. G. — An unusual basal cell with two 

 septa and an abnormally large footlike base. H, J, L. — Typical basal 

 cells of conidiophores. I. — Upper portion of an underdeveloped coni- 

 diophore bearing three spores on sterigmata arising directly from the top 

 of the main axis. K. — Tip of an ultimate branch with two sterigmata- 

 bearing conidia. M. — Basal cell of a conidiophore from teosinte with 

 septum formation progressing by the centripetal extension of a cellulose- 

 pectose ring 122 



25. A. — Conidiophore from sorghum, partly matured and bearing few conidia. 



B. — Conidiophore from teosinte, nearly mature, with extensive system 

 of branches bearing many conidia. C. — Typical conidia from sorghum. 

 D. — Typical conidia from teosinte. E. — Typical conidia from teosinte 

 which have germinated in dew on the leaf smface. F. — Conidium 

 from teosinte germinating by an extensive branched hypha when main- 

 tained in dew at 7° C. G. — Conidium from teosinte germinating while 

 still attached to its sterigma. H. — Typical conidia from maize, showing 

 common variations in shape and size. I. — Two conidia fi'om maize just 

 beginning to germinate in rain water. J. — Two conidia from maize 

 germinating in sterilized brook water maintained at 8° C. K. — Coni- 



