1919] Colt-Hodgson: Abnormal Shedding of Washington Navel Orange 303 



configuration of the navel end, renders it reasonably certain that 

 infection occurs some time after the style has been shed. The spores 

 are probably blown and find lodgment in ragged open navels where 

 they are held in the crevices till enfolded and overgrown by the rapidly 

 developing ovary (pis. .'54, 37). Inasmuch as the configuration of the 

 navel as well a.s its size and degree of insertion are exceedingly variable, 

 it is evident that only in a comparatively small and variable number 

 of eases are the spores or mycelium so situated as to permit germina- 

 tion or growth. Alternaria citri is a weak parasite and cannot pene- 

 trate the unbroken skin of an orange. While it is not capable of pro- 

 ducing any widespread breakdown in the tissues of immature oranges, 

 it is able, after introduction into the fruit, to bring about a certain 

 stimulus or irritation which, according to our theory, results in abscis- 

 sion of a certain proportion of the young fruits. It is certain that as 

 the fruits grow and approach maturity the abnormal size, premature 

 ripening, and extra deep color are the direct results of this stimulation. 

 It is also considered highly probable that a certain proportion of the 

 splitting or dehiscence of the carpels which is so serious in interior 

 valleys is connected with the stimulation of these infections. 



Referring again to the wide distribution and general prevalence of 

 Alternaria spores in the air. it is evident that the spores may be trans- 

 ported in large numbers for great distances. The source of infection 

 is by no means limited to the vicinity of orchards. The fungus grows 

 readily as a saphrophyte on dead leaves, weeds, twigs, and other plant 

 debris and it is entirely possible for spores to be brought in from 

 forest areas in the mountains many miles away. Spores have been 

 taken in the desert far from cultivated crops. In the dry air of the 

 San Joaquin Valley the black rot oranges which fall under the trees 

 are not immediately decomposed by Penicillia, Fusaria, and other fungi. 

 They tend to mummify and after the Alternaria spreads through the 

 interior it comes to the surface, and the spores there formed give these 

 mummies a black color, as shown in plate 38. These mummies, together 

 with the large number of abscissed styles from the blossoms, undoubt- 

 edly furnish a greatly increased supply of spores at the critical time 

 in the development of the fruit. 



A rot of apples occurring in Colorado 37 has been described as caused 

 by an undetermined species of Alternaria. Judging from the draw- 

 ings presented in plate 4 of Longyear's publication, the fungus is very 

 similar to if not the same as that with which we are dealing. Moreover, 



37 Longvear, B. O., A New Apple Rot, Colorado Agr. Exp. Sta. Bull. 105, 

 1905. 



