Mar. i, 1924 
Morphological Characters of Alternaria mali 
703 
more than twice as long, mostly unbranched except that conidiophores 
may spring from them. Aerial hyphae either on apple leaves kept in 
moist chambers or in corn-meal agar cultures are nearly hyaline to light 
amber, often geniculate, branched, occasionally joined together (reticu¬ 
late), segments relatively much longer than in surface hyphae 3 to 5 n 
wide, length quite variable 5 to 25 /jl or longer, often constricted at the 
septa, especially when old. 
In old cultures the hyphal segments often become swollen to form 
chains of chlamydosporelike bodies. 
The conidia (fig. 1 and PL 1, C) on apple leaves form tiny black masses, 
which separate easily from the leaf. In corn-meal agar cultures, chains 
of conidia form a dark carpet-like mass over the surface of the medium. 
Conidia also occur to some extent scattered through the aerial hyphae 
and at the surface of or in the medium. They are light amber to very 
dark olive or nearly black, those produced just above the surface of the 
medium being the darkest and those produced on aerial hyphae well 
above the medium being the lightest. The typical arrangement is 
in simple or branched chains. Septation may be transverse and longi¬ 
tudinal (muriform), with constriction at the septa especially when old. 
Verrucose outer walls (fig. 1, C) are common and sometimes the rule. 
The number of septa vary with the size and shape of the conidium. 
In general, conidia produced along the surface of or in the artificial 
culture medium are much longer and narrower than those produced in 
chains projecting above the medium or on aerial hyphae (fig. 1, D, E). 
Narrow conidia are more often without longitudinal septa. 
The conidiophore subtending the first-formed conidium of a chain 
is produced at approximately right angles to the hypha (fig. 1, A). 
It is often short and nonseptate or one-septate, but it may be long and 
multiseptate (fig. 1, B). Usually, it is broader than the hypha 
from which it was produced. When the conidium separates from it, 
a dark-colored scar is seen at the point of attachment (fig. 1, B). It is 
usually smooth with a swollen apex, but in older cultures it may be at 
least as many as three times geniculate, each joint denoting the origin 
of a chain of spores (fig. 1, B). These conidiophores of the initial 
spores of the chains are usually fasciculate on apple leaves in nature, 
and are often so in artificial cultures. 
The conidiophores (isthmi) supporting subsequent members of the 
chain are outgrowths from terminal (distal) segments of conidia, or in 
branched chains, lateral outgrowths from nonterminal segments. They 
resemble the conidiophore of the initial conidium very closely. They 
are swollen at the tip, may be nonseptate or multiseptate, short or long, 
straight, angled, or geniculate (fig. 1, B). In color they range from 
nearly hyaline to olive, the former predominating except when old. 
In all the following measurements and in all consideration of septation 
the conidiophore or isthmus is not regarded as part of the conidium. 
Unless otherwise specified the word “septate” means “transversely 
septate.” In each series, the measurements (in microns) are of 50 
conidia taken at random. Conidiophores were measured at their 
greatest width. 
