117 
Septa Differences of means of septa 
He Noss) andi 3)2-2. Yoyo te eereithe a pshe 0.27 + .16 
INosiy dr and atsit: vhs acces at 0.80 = .12 
lal INGoysseeibernl Ghee cogaueccnmor SOD Great 
Fe NOst Seandinll Oneness (0,2) = itil 
It is to be noted that the differences between Nos. 15 and 16 are quite 
as large relative to the probable error as are the differences between Nos. 1 
and 3. Ravn(91), speaking of three species of Helminthosporium, says that 
the septa are very variable, and that specific differences can not be derived 
from them. Very abnormal septation was frequent; for example, on green- 
wheat agar (Fig. 14) and other uncongenial media. 
Fic. 14.—Various abnormal conidia of 
H. No. 1 as grown on green-wheat agar. 
Conidial shape-—The shape of the conidia, together with their size and 
septation, are in the genus Helminthosporium the three most-used charac- 
ters in description. Indeed in published descriptions of many species these 
are the only important characters mentioned, and often one or more of these 
is lacking. Conidial shape in certain species is very characteristic, partic- 
ularly in H. inaequalis, H. geniculatum, H. ravenelii, and also in my H. 
No. 29. Much stress has been laid on conidial shape as a means of distin- 
guishing certain cereal Helminthosporiums, particularly in distinguishing 
H. satwum from H. teres. 
Merely to look at two lots of conidia with the microscope, even with 
the aid of a comparison ocular, is not a satisfactory means of ascertaining 
the prevailing conidial shape. Many strains of Helminthosporium vary 
greatly as to conidial shape, and conidia of one shape are mixed with those 
of another (Pl. XIX—XXI). The important question is, what is the 
relative frequency of the various shapes? But before any fair estimate of 
this can be made, standards must be established as to what are the essen- 
tial characters of the various shapes. 
One factor of preponderating influence in determining these conidial 
shapes is the position that the point of greatest diameter occupies on the 
