676 
Journal of Agricultural Research 
Vol. XXIV, No. 8 
Soon these spots increase in length and width, the center in the meantime 
fading to almost white or light straw color. In this way the appearance 
described by Heald and Wolf (54) is brought about. (PI. 10, A, B.) 
At this stage the lesions are of the simple “eye-spot” type. Under 
certain conditions, apparently when the parasite is thriving most 
luxuriantly, the diseased areas become greatly enlarged, sometimes 
occupying the entire width of the leaf blade of Bermuda grass for a 
distance of one centimeter or more. When such development occurs 
the dead areas usually show a number of roughly concentric brown 
markings, evidently corresponding to successive positions of the margin, 
and giving the areas a distinctively zonate aspect. With the multi¬ 
plication of the smaller lesions and the extension of the larger ones, a 
large proportion of the leaves are killed outright long before the end of 
the season. Previous to this the sporophores of the fungus make their 
appearance singly or in pairs over the larger dead regions always at 
some distance from the margin of the surrounding green tissue. The 
conidiophores are distributed rather sparsely in comparison with the 
crowded spacing of the homologous structures of many congeneric forms, 
although not actually few in number. 
The sporophores of Helminthosporium giganteum (PI. 10, Ea, b) are 
the largest of those of any species studied by the writer, the measure¬ 
ments of the Florida material agreeing well with those given in the 
original specific description. The septa are mostly spaced with consider¬ 
able regularity, at intervals varying commonly from 25 to 40 ju. Usually 
the scar marking the point of attachment of the first spore is found 140 
to 250 jLt from the base, and successive scars associated with genicula- 
tions, usually not pronounced, occur at intervals of approximately 40 yn. 
The conidia (PI. 10 Ca-d), which are produced in relatively small 
numbers, are easily the most massive of those of any species of Helmin¬ 
thosporium hitherto described, and are probably among the very largest 
produced by any group of fungi. Individual spores were found exceeding 
considerably in length even the generous measurements given by Heald 
and Wolf, the one figured in Plate 10, Cc, for example, measuring 385 m 
in length and 2 ijit in diameter. The volume of a spore of such dimensions 
is several hundred times greater than the volume of spores of molds that 
are not by any means regarded as minute fungi, while'on comparison with 
some of the smallest types, like species of Actinomyces, ratios approxi¬ 
mately I to 300,000 may be obtained. The writer has found it possi¬ 
ble, after staining with eosin, to make out with the naked eye, spores 
approaching the dimensions given. 
Besides being^the largest, the conidia of Helminthosporium giganteum 
also, perhaps, are the shortest-lived conidia of any species of Helmintho¬ 
sporium discussed in this paper. If the spores from a group of fructifica¬ 
tions which are still actively proliferating new conidia are mounted in 
water, a large proportion will be found to contain one or more dead 
segments. After spore production in a group of fructifications ceases 
all of the conidia will contain dead segments, and in a relatively brief 
period, probably not exceeding two weeks, only a small number will still 
show living segments. To this lack of longevity, together with the 
production of spores in small numbers, the comparatively restricted 
occurrence of the parasite probably may be attributed. 
The spores of Helminthosporium giganteum^ while alive, are altogether 
hyaline, colorless, and filled with homogeneous protoplasm. The char¬ 
acterization of these structures by Heald and Wolf in the words, “ pale 
