490 SPECIAL PLANT PATHOLOGY 



The fungus is largely propagated by its urediniospores, which are 

 ellipsoid to spheric in form and measure 24-35^1 by 21-26/i. The 

 spore wall is thick and spinulose. The teliospores resemble in form 

 the urediniospores and measure 20-35JU by 18-25/x. Their walls are 

 chestnut-brown and uniformly thickened with terminal germ pores 

 and are papillate. As the adult plants may be infected, the disease 

 may spread rapidly during the growing season. 



The disease can be controlled undoubtedly by growing rust-resistant 

 varieties of carnations. The leaves should be kept away from the 

 moist soil by simple V-shaped wire mesh supports and lastly fungi- 

 cides, such as a solution of copper sulphate (i pound copper sulphate 

 to 20 gallons of water), might be used with success, Duggar also rec- 

 ommends the use of potassium sulphide i ounce to a gallon of water. 

 Sub-irrigation has been practised. 



Cacao (Theobroma cacao, L.) 



Brown-rot (Thyridaria tarda, Bancroft). — A number of different 

 organisms have been thought at different times to cause the brown rot 

 of the chocolate pods, but Bancroft in 191 1, an authority on the sub- 

 ject, ascribed the disease to the above-named fungus. Circular brown 

 patches appear on the chocolate fruits along the grooves that seam 

 the surface. The disease spreads rapidly and the fruit falls in from six 

 to ten days from the time that it is first infected. When the spots are 

 2 cm. in diameter, their center becomes marked by wounds in which 

 a brownish-gray mycelium appear. Wounded fruits are especially 

 open to infection through the abraded surface and the seeds, or beans, 

 are sometimes involved and are destroyed completely. The disease is 

 widely spread in the eastern and western tropics (in Jamaica, Santo 

 Domingo and the Philippines). It may be controlled to some extent 

 by burning all diseased fruits, busks and prunings. 



Pink Disease {Corticium lilaco-fuscum, Berk & Curt.). — The genus 

 Corticium belongs to the family of Thelephorace^, which includes 

 the smothering fungi of the genus Thelephora. The leathery hymeno- 

 phore of Corticium is membranous, fleshy, waxy with clavate basidia 

 with four sterigmata. The basidiospores of our cacao fungus are 

 sessile on the basidia. It attacks the younger branches of the chocolate 

 tree covering them with a pinkish incrustation, which spreads over 



