14 
BULLETIN 395, U. S. DEPARTMENT OF AGRICULTURE. 
Conidia. — The conidia (fig. 5, a and b) are borne acrogenously, 
either singly or in short chains which may be branched when con- 
ditions especially favor sporulation. The spores appear first as small, 
rounded, hyaline projections from the apices of the conidiophores. 
These bodies rapidly enlarge, assume the ellipsoidal shape of the 
immature spore, and become ab jointed by septa from their sporo- 
phores. The mature conida are very well described by Yon TMmen 
(1879, p. 13). 
* * •* sporis fusoideo-ovatis, utrinque obtusiusculis vel raro vertice subacutatis, 
rectis, non vel obscure uniseptatis, diaphanis, 20 mm. long., 5-6 mm. crass., dilute 
fuscescentibus. 
If divided, the spores tend to be slightly constricted in the middle. 
The cells are very similar in size and shape, except that the basal ones 
tend to be slightly thicker and the apical less obtuse. In nature, 
normal mature conidia are fairly uniform in size. When they are 
produced in chains, the mature apical spores are indistinguishable in 
size and shape from the basal. The results of the measurements of 
240 conidia from various sources are summarized in Table III. 
These measurements agree closely with those of Von Thumen (1879) 
except that the spores average 4.3 n shorter. 
Table III. — Measurements of conidia of Cladosporium carpophilum. 
Source. 
Number 
measured. 
Average measure- 
ments (microns). 
Source. 
Number 
measured. 
Average measure- 
ments (microns). 
Length. 
Breadth. 
Length. 
Breadth. 
Fruit 
10 
50 
50 
20 
20 
16.7 
14.4 
15.5 
16.8 
14.9 
5.0 
5.2 
5.2 
4.8 
4.2 
Leaf lamina 
Do 
20 
20 
20 
20 
16.6 
16.2 
15.6 
16.5 
17.2 
4.9 
Do 
4.7 
Overwintered twig 
Do.... 
4.8 
Do 
5.1 
Twig of current 
Leaf midribs 
10 
4.5 
Do"'..'..'....... 
15.7 
4.9 
1 
PHYSIOLOGY. 
The objects of the physiological studies were (1) to gain a clearer 
comprehension of the responses of the fungus to its environment 
under controlled conditions, in order better to understand its behavior 
in nature, and (2) to furnish a further basis for the identification of 
the organism by other investigators. 
Cultural Studies. 
By means of the poured-plate method the fungus was readily 
isolated from freshly produced conidia from fruit, twig, or leaf 
lesions. At first, considerable difficulty was encountered, because 
the scab fungus developed so slowly that it became overrun by sapro- 
phytes. It was possible, however, to minimize the contamination by 
