May 1, 1920 Philippine Downy Mildew of Maize loi 



reduplications, virescences, and other abnormalities of the various catego- 

 ries of monstrous growths that are recognized in teratology. Less 

 frequently also the vegetative parts of the infected plants show abnor- 

 malities induced by the disease, fasciations and torsions of the stem 

 (PI. 17, B) and shank (PI. 19, A) being most common. These abnormal- 

 ities, of course, are frequently induced by other diseases and by unfavor- 

 able conditions of the environment, but their occurrence in connection 

 with the downy mildew is so common as to form an accessory symptom 

 of diagnostic value. 



One other marked effect of the disease is the delaying of ear produc- 

 tion. Normal plants in a plot invariably will bear well-developed ears 

 in the "milk" or "glazing" stage before the diseased plants have devel- 

 oped ears to the "silking" stage. 



It should be noted that the loss of chlorophyll and the consequent 

 yellowish or whitish color of the marked areas, which is so characteristic 

 a symptom of the disease, is by no means permanent but serves particu- 

 larly to point out the earlier stages of the attack. As the diseased plant 

 matures, however, and the fungus begins to terminate its period of 

 spore production, the marked areas become more and more green, the 

 contrast between the normal green and the paler portions of the leaf 

 becoming less and less distinct until, finally, in plants less heavily at- 

 tacked, the marked areas may so far regain their green color as to be 

 almost indistinguishable from the normal. 



All these plants which show the disease at a late date do not necessa- 

 rily undergo rapid destructioft as in the cases of early attack. On the 

 contrary, although the plants are more susceptible to the secondary 

 infections than are their healthy companions, they may mature along 

 with them, drying and withering at a date only slightly earlier than 

 normal. In some cases the infected plants seem stimulated by the 

 downy mildew to prolonged activity and show persistent and excessive 

 growth of husks, or of bracts in the deformed tassels, after adjacent 

 plants are withered and dry (PI. 19. A). 



The susceptibility to infection is greatest in the young seedling and 

 decreases markedly as the plant develops, so that by the time it has 

 tasselled and is forming ears its tissue is, as a rule, too mature and resistant 

 to permit infection. If, however, as is frequently the case in some varie- 

 ties, the main plant sends out secondary shoots or suckers, these may 

 rapidly become infected (PI. 19, ^), and through them the infection 

 may spread to the main plant even though it is so far matured as to 

 have its kernels hardening. 



When attacked in this way, the mature plant shows symptoms different 

 from any of those described above. The lower leaves are inconspicu- 

 ously marked throughout their length with narrow, pale, yellow-green 

 to rusty green stripes, which are not continouous but are irregularly 

 broken and interrupted. On the middle leaves, as a rule, the markings 



