88 Problems of Economic Biology in East Africa 



In East Africa owing to the very much nioister conditions the plant 

 reaches maturity far sooner and flowers and dies in its fourth year. The 

 leaves, which are ready for cutting at the end of three years, contain 

 very much less sugar, and it was found on analysis that even in the dry 

 season not sufficient sugar was present to render the fermentation of the 

 waste practicable, without going to the expense of concentrating the 

 liquid first. So far, no sisal planter has seen his way to do this, and the 

 subject has received no further attention, though without doubt both 

 sisal waste and coffee berry pulp could be utilised for the production of 

 alcohol. 



In a very wet rainy season at the coast the ring-spot disease, due to 

 Collet otrichuin agaves Cav., has been recorded, and nearly always under 

 such conditions a sun-scorch also takes place in which large irregular 

 patches, red in colour, are produced, rendering decortication difficult 

 or impossible. The spores of Colletotrichum agaves can be disseminated by 

 air currents. During the rainy season when this disease appeared at the 

 coastal plantations, a yellow bacterial blotch occurred in a plantation 

 near Nairobi and by the amount of gum produced in the tissues decortica- 

 tion was rendered impossible. The sunken yellow areas were produced 

 on the upper half of the leaves and varied greatly in size, from a small 

 speck to a patch several inches in length. The bacteria entered through 

 the stomata and the organism, a bacillus, was isolated and produced the 

 disease by inoculation, but was not studied in detail. The blotch ceased 

 to spread on the cessation of the rains and is not likely to cause much 

 damage except in a prolonged and abnormally heavy rainy season. 



No damage as yet has been caused by insects, but larger beasts such 

 as the porcupine do, in certain parts, cause considerable loss by eating 

 off the entire tops of young plants, thus reducing the length of the leaves 

 and consequently the fibre. 



IV. Coffee. 



Coffee growing is one of the staple industries of the highlands of East 

 Africa, and has steadily increased since Coffee arahica L. was first planted 

 by missionaries a quarter of a century ago. Of native coffee, only one 

 occurs in the country, namely, C. nandiensis, which is found on the steep 

 banks of rivers at an altitude of over 7000 feet and is a shade-loving 

 plant. C. robusta is the native coffee of Uganda. It is to be noted that 

 there is no resting period such as occurs in Rhodesia, where once every 

 year all the leaves fall from the tree. In East Africa coffee is not deci- 

 duous, but is continually producing more leaves, rapidly during the rains, 



