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Pomona College Journal of Economic Botany 



There are millions of these conidia formed within each acervulus. (Fig. 19 

 A, B.) As stated above the spores (Fig. 19 C, D, E) are oblong or oval, but 

 much longer than the diameter. In mass they appear cinnamon brown or 

 even dark, but under the lens they are apparently colorless, containing minute 

 granules and several oil globules, as shown in the figures. They are formed 

 as small buds (conidia) upon the ends of short conidiophores and break off 

 very easily when mature. There may be seen all stages of these forming 

 conidia and conidiophores in a single acervulus, but all will mature before the 

 fungus has finished its mission in life. It is not over-stepping the mark- 

 to say that each acervulus may produce many thousands of spores, all of 

 which will germinate under favorable conditions. The acervuli may be 

 produced upon any surface of a twig, fruit, or leaf in numbers sufficient 

 to prove that the mycelium has penetrated every cell beneath. (Fig. 19 B.) 



Prof. Rolfs' technical description is as follows : "Acervuli located on the 

 surface of the leaf, twig, or fruit; 90-270 u in diameter, erumpent, super- 

 ficial. Shape various, not uniform, occuring on either surface of citrus 

 leaves ; disposed irregularly or in more or less concentric lines ; pale to dark 

 colored. On tender lime twigs, tender lemon twigs, lemon fruits, and lime 

 fruits, pale colored, dull red in masses, confluent. Epidermis breaks irregu- 

 larly." 



"Setae fuliginous, ranging in length from 60 to 160 u, frequently once or 

 twice septate, disposed at margin of acervuli. Frequently absent, and on 

 tender lemon twigs, tender lime twigs, lemon fruits, and lime fruits usually 

 absent." 



"Conidia broadly oval or oblong, 10-16 u by 5-7 u, hyaline; size variable in 

 same acervulus, usually with one or two oil drops. Developing from a well 

 defined stroma ; basidia, 3-8 u. In moist chamber the conidia stream from 

 the break in the epidermis." 



"Intra-basidial setae, variable 8-30 u by 3-6 u, cylindrical or sometimes 

 enlarged at distal end ; hyaline." — U. S. Dept. of Agrcl. Bull. 52, p. 16, Mar., 

 1904. 



DESTRUCTIVENESS 



As has been stated before, the first appearance of the disease upon the 

 orange, in a seirous way, was upon the foliage and especially on the fruit- 

 bearing wood for the next season, although much of the present bearing 

 wood was completely killed and the fruit fell to the ground. The photo- 

 graph (Fig. 9) will give some idea of this attack. It will be seen that the 

 leaves have died in patches all over the outside of the tree. The bare 

 twigs at the top shows an earlier attack which dropped all of the leaves. 

 Figure 18 A shows a branch taken from the top of a sweet orange tree a 

 week after the infection was first observed upon the tree. Figure 14 A shows 

 a typical case of fallen leaves and fruit. This photograph was taken under 

 the tree shown in Figure 14 B a week after that photograph was taken. It 

 will give some idea of the severity of the disease and an idea of what it 

 means to an orchardist. 



