J02 Journal of Agricultural Research voi. xix. N0.3 



are similar in character but occupy principally the more distal part of 

 the leaves, while the upper leaves are either entirely unmarked or have 

 the striping confined to a small part of the leaf tip. Since most of the 

 parts of the plant are matured, they show no change in form as a result 

 of the infection, but the ear, if not mature, may elongate slightly and 

 project from the husks at the tip (Pi. 19, B). It is to be noted that a 

 plant thus attacked, in contrast to those previously described which 

 are infected early, is marked least extensively and conspicuously on the 

 upper leaves and most extensively on the lower leaves, has ears little if 

 at all altered, and bears no conidiophores on the marked areas. 



The production of conidiophores on the diseased plant is, of course, a 

 symptom valuable in recognizing the disease (Pi. 21). Unfortunately, 

 however, the process of conidiophore formation takes place almost 

 exclusively at night and is controlled largely by conditions of the environ- 

 ment. The details of this relationship will be given later. It need only 

 be said here that a plant may be attacked heavily by the fungus, the 

 mycelium of which invades its tissues throughout, and may show the 

 changes of color and growth which are characteristic of the disease and 

 yet never form conidiophores and conidia unless external conditions are 

 favorable. 



A comparison of the symptoms of the Philippine downy mildew with 

 those which characterize the downy mildew of maize in other countries 

 shows many similarities. 



In the closely related Javan mildew of maize, Palm (75) has recognized 

 three distinct sets of symptoms. Of these, the symptoms of type A 

 correspond in general to the description given above for plants attacked 

 early in life, while the symptoms of type B correspond to those of plants 

 attacked later. Type C, however, is characterized by narrow, incon- 

 spicuous stripes of a dark brown color running, the -full length of the 

 lowest leaves and decreasing in extent on successively younger leaves 

 until the last marked leaves show these stripes at the tip only, while the 

 still later leaves are of the normal green throughout. 



No specimens corresponding exactly to the description and illustra- 

 tions of Palm's type C have been seen in the study of the Philippine maize 

 mildew. Occasional stripings of this sort have been observed on the 

 lower leaves of plants whose upper leaves showed the general or restricted 

 discoloration already described. Maturing plants infected through 

 suckers have shown inconspicuous, d!P.rk orange-colored stripings, exten- 

 sive on the upper leaves and decreasing in area on the lower. In no case, 

 however, has an immature plant been seen with these dark markings of 

 the leaves decreasing oft successively younger leaves until the latest are 

 untouched. 



For the Philippine maize mildew it does not seem justifiable to attempt 

 to make such hard and fast categories as the types A, B, and C of Palm, 

 although the symptoms shown by many plants can be more or less 



