May I, igao Philippine Do-wny Mildew of Maize 1 1 5 



mature spores normally follow when it is free, it is obvious that a mount 

 of spores usually comprises a motley collection of shapes and sizes, only 

 a comparatively small number of which represent the characteristics of 

 the normal and mature spore. 



Moreover, aside from these variations which mark the normal devel- 

 opment of the spore, there are also changes in size and shape resulting 

 from abnormal conditions such as the sudden checking of development 

 by unusual drying of the necessary layer of moisture on the leaf. 



The size and structural characteristics of the conidiophores also vary 

 markedly with attendant environmental conditions. The normal order 

 is for primary, secondary, and tertiary branches to form before the 

 sterigmata develop and begin to bud out the spores. If the gradual 

 drying of the film of moisture on the leaf surface begins to check this 

 process before its completion, however, sterigmata formation and spore 

 production ensue prematurely, arid conidia may be borne on the sec- 

 ondary or primary branches of the conidiophore (PI. 24, I), or even on 

 the apex of the main axis itself. Similarly, the growth of the basal cell 

 and main axis may be curtailed (PI. 24, E). Obviously, as a result of 

 these changes, the height of the conidiophore shows a corresponding 

 alteration. 



Finally, after it has lost its conidia, the conidiophore shrivels and is 

 dried to an almost unrecognizable mummy by the morning sun. 



Since it appears highly probable that similar variations in size and 

 structure occur also in the other oriental mildews, it is difficult to make 

 any adequate comparison from the data available. To permit accurate 

 comparison one should have descriptions and illustrations of material, 

 or the material itself, collected under the optimum conditions, which in 

 the case of the Philippine downy mildew occur on cool nights with heavy 

 dew or persistent rain from 2 to 4 a. m. 



In the light of this fact, Miyake's {14) data are valuable, as he recog- 

 nized that conidiophores and conidia were produced at night, and his 

 drawings show that he illustrated excellent material. Most investi- 

 gators, however, failed to realize this, and their material, as their descrip- 

 tions and drawings show, was inadequate and scanty. 



When one compares the available data, inadequate though they be, the 

 following points are apparent. The Philippine and Javan Sclerosporas 

 are alike in that the conidial phase is the only one yet known. 



The conidiophores of the former closely resemble those of Sclerospora 

 javanica Palm both in size and structural characteristics, such as the basal 

 cell, the main axis, the branch system, and the ultimate sterigmata. On 

 the contrary, the conidia of the two forms are noticeably different. In 

 the Javan fungus they are oblong rotund in shape and measure 19 to 26 /z 

 in length by 15 to 20 /x in diameter, while in the Philippine mildew they 

 are elongate ellipsoid, elongate oval, or rounded cylindric and markedly 

 longer, most of the conidia encountered measuring about 34 ^i in length 



