DISEASES OF HEVEA 233 



and perithecia. The conidial form of the fungus was named 

 Fusicladium macrosporum by Kuijper, Passalora Hevece by 

 Massee ; it was regarded as pertaining to the genus Scolecotri- 

 chum by Griffon and Maublanc, a conclusion with which Stahel 

 agrees. The conidiophores when young are short unicellular 

 brown hyphae thickened at the base, penetrating the epidermis 

 from subepidermal mycelium ; this form appears on the young 

 translucent leaves. On somewhat older leaves the conidiophores 

 are many-celled, elongated, and arise from a pseudo-parenchy- 

 matous base. The conidia are formed singly and terminally, 

 measure 20-65 X8-12 microns, normally are divided into a wider 

 basal cell and an elongated terminal cell, and are more or less 

 bent or spirally twisted. 



The pycnidial form was first described as Aposphcsria Ulei, 

 Hennings. The pycnidia occur freely as small black dots on 

 the surface of leaves 1-2 months old, mostly on the upper side. 

 They are roughly spherical, with an apical pore and little or no 

 trace of a papilla. The pycnospores are 5-10 microns long, 

 2 microns wide at the ends, narrowing to i micron in the middle. 



The perithecial form was described by Hennings as Dothidella 

 Ulei, but is placed by Stahel in the Sphaeriaceas in a new genus 

 Melanopsammopsis. The perithecia begin to take the place of 

 the pycnidia some two months after the leaves are full grown. 

 They occur in rings of 3-4 mm. or rounded groups of 1-2 mm. 

 diameter, are smooth, carbonaceous, and closely resemble the 

 pycnidia in form and size. The ascospores are hyaline, two- 

 celled (one larger than the other), constricted at the septum, 

 18-22 X 6-8 microns. 



A species of Botrytis is common as a parasite of the fungus 

 in all its stages. 



Infection. 



The conidia germinate in water in 1^-2 hours and cannot 

 withstand more than 15-20 hours' exposure in a desiccator. 

 Stahel found viable ascospores to be rare, and unable to with- 

 stand more than four to six hours of desiccation. According 

 to his observations the pycnospores germinate very weakly and 

 appear to have no part whatever in the spreading of the disease, 

 nor do the ascospores exhibit more than weak powers of infection. 



The conidia produce germ-tubes which penetrate the cuticle 

 and give rise to a sub-cuticular hypha, from which branches pass 

 between the cells of the epidermis and produce an intracellular 

 mycelium. Infection takes places only in the very young and 

 tender organs. Leaves are most susceptible in the first four days 

 after the opening of the buds, and lose their susceptibility after 

 seven days' growth. The first sign of infection is a yellowish 

 spot which appears in about five days, and one to two days later 

 the conidial stage appears, followed by pycnidia ten to twelve 

 days after infection. On the fully developed leaves the pycnidial 



