May 1. 1920 Philippine Downy Mildew of Maize 107 



and the lobed, contorted, irregularly branched, gnarled, and crooked 

 hyphae which run in and out among the mesophyll cells of the leaves 

 (PI. 23, A). 



The first kind seem to serve for communication from one part of the 

 host to the other and can be followed for considerable distances even in 

 longitudinal section (Pi. 23, B). The second kind appear to act as a 

 means of establishing connection with the mesophyll cells, especially with 

 the bundle sheath, in order to derive nutriment therefrom, since they are 

 found in every possible crevice in the most intimate contact with the host 

 cells (PI. 23, A, E). 



Haustoria are produced by both types of hyphae but are best developed 

 or most pronounced on the crooked assimilatory hyphae among the 

 mesophyll cells in the leaf. In shape the haustoria are simple, papillate 

 to tubular (PI. 23, F, G), as a rule, but they may be somewhat lobed 

 (PI. 23, H). In no case, however, were such markedly digitate haustoria 

 seen as those figured by Rutgers (19, PL 6) for the Javan Sclerospora. 

 The haustoria penetrate portions of the host cell wall, against which the 

 hyphae are closely appressed, and project into the lumen. Not only the 

 cells of the mesophyll, bundle sheath, and pith are penetrated, but also 

 occasional cells of the epidermis (Pi. 23, E, c) and even the xylem (PI. 23, 

 E, h). 



In any case, the haustoria accomplish the penetration of the host cell 

 without occasioning its collapse, although the wall often is wrinkled and 

 the turgidity of the cell decreased, apparently through the extraction of 

 its contents by the parasite. The chloroplasts of the parasitized cells 

 are gradually destroyed through the action of the fungus, with the result 

 that the badly infected areas lose their green hue and assume the pale 

 yellow or whitish color symptomatic of the disease. Occasionally the 

 host cell surrounds the haustoria of the parasite wnth a thick wall 

 (PI. 23, F), as if in protective response to the injurious stimulus of the 

 fungus, a condition observed also by Butler (5) in Sclerospora graminicola 

 (Sacc.) Schroet. on Pennisetum. 



The hyphae are hyaline, rarely if ever septate, thin-walled, with gran- 

 ular content, and vary greatly in size, 8 /x being perhaps the most common 

 diameter. The haustoria are similar in structure and usually about 8')u 

 long by 2 ju in diameter. 



In the larger air chambers which underlie the stomata, the mycelium 

 develops somewhat irregular clusters of stout branches (PI. 23, E, a), 

 from which, under favorable conditions, the conidiophore initials arise 

 and grow out through the stomata to produce the conidiophores. 



CONIDIOPHORES 



Conidiophores may be said, in general, to be produced on any part of 

 the plant save the roots. They occur on the main stem, on the leaves, 

 leaf sheaths, and car husks, and on the main axis, branches, and glumes 



