17 



Plantarum.* At that time the number of species of those 

 orders recorded as occurring in Tropical Africa might have been 

 estimated at somewhat over 700. Volume III. contains 1,134 

 species. Allotting to volume IV. approximately the same number 

 of species, there was therefore a margin for 400 additional species, 

 corresponding to an increase of 60 per cent. But so extraordinary 

 was the accession of new material during the progress of the 

 preparation of volume IV., that in the end the number of species 

 of the orders reserved for it rose to 2,176, double the original 

 estimate. That, of course, necessitated the subdivision of the 

 volume into two parts, each equalling in size an ordinary volume. 

 The increase was very unequal in different orders — as will be 

 seen from the list given below — varying in the larger orders (of 

 over 100 species) from slightly over 50 per cent, in Solqjiaceae to 

 well over 300 per cent, in Apocynaceae, and almost 600 per cent, 

 in Loganiaceae. The significance of these figures will perhaps 

 more readily be grasped when we consider that the increase from 

 813* species known before 1891 to 2,176 known at present means 

 that for every three species then known, five species have since been 

 added ; and if we assume that the same proportions hold good in 

 the case of the orders dealt with in the first three volumes of the 

 Flora of Tropical Africa, these orders would, if worked out at 

 present, fill at least eight volumes. That this is by no means an 

 exaggerated view may be seen from the fact that the Tropical 

 African Myrsinaceae and Sapotaceae, which in the third volume 

 (1877) numbered 11 and 23 species respectively, are, in recently 

 published monographs, represented by 36 and 92 species respec- 

 tively. 



"This phenomenal increase of our knowledge of the flora of 

 Tropical Africa since 1891 has been due to several causes. Old 

 collections of very considerable extent which had only casually 

 and partially been studied have now been worked up systemati- 

 cally {e.g., Barter's West African, Schweinfurth's Sudan, and 

 Welwitsch's Angola collections) ; fresh collections have poured in 

 as new countries were opened up or the establishment of botanical 

 stations in the older colonies facilitated a more exhaustive 

 exploration of their neighbourhood ; finally it was just then that 

 Germany started with remarkable and well-directed energy on the 

 botanical survey of her colonies, with the result that in not a few 

 orders 50 per cent, or more of all the additions from recent 

 collections are due to her enterprise." 



Since it is of the first importance from the practical point of 

 view, that plants of commercial value should be identified both 

 botanically and under their native names, it is necessary that all 

 specimens collected in the country should be preserved as carefully 

 as possible and that the native names should in all cases be 

 recorded. 



* These figures include a number of species which, although known prior 

 to 1891, were not recorded from Tropical Africa until after 1890. To make out 

 their exact number would have taken more time than could reasonably In- 

 spared ; but it probably does not exceed 70 or 80, so that the species of the 

 orders inquestion which were known from Tropical Africa at the end of 1 891 1 

 may be estimated as somewhat over 7 ( »'V 



3338S JJ 



