14 



BULLETIN 395, U. S. DEPARTMENT OP AGEICULTUEE. 



Conidia. — The conidia (fig. 5, a and h) axe 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 Von Thiimen 

 (1879, p. 13). 



* * * Bporis fusoideo-ovatis, utrinque obtusiusculis vel raro vertice subacutatis, 

 rectis, non vel obscure uliiseptatis, diaphanis, 20 mm. long., 5-6 mm. crass., dilute 

 fuscescentibus. 



If divided, the spores tend to be sHghtly constricted in the middle. 

 The cells are very similar in size and shape, except that the basal ones 

 tend to be sUghtly 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 Thiimen (1879) 

 except that the spores average 4.3 /i 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 

 10 



16.6 

 16.2 

 15.6 

 16.5 

 17.2 



4.9 



Do 



4.7 



Overwintered twig 

 lesions 



Do... 



4.8 



Do 



5.1 



Twig of current 



Leaf midribs 



4.5 



Do 



15.7 



4.9 











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 



