times. When a certain species was not recorded for a trip it was 

 concluded that it did not occur in the island at the time that trip 

 was made. Repeatedly, also when the investigations ware not made 

 in the same locality, one may read in the publications 1) that plants 

 were not present at the time of a former expedition, that they 

 have recently appeared, that they liave become more common or less 

 frequent, that the character of the vegetation was modified since 

 the last investigation. 



It need scarcely to be said that a mere list of names of spe- 

 cies, which were found at a few trips made with large intervals, is 

 of little value for an investigation on the gradual renewal of a quite 

 or almost destroyed flora. If such a list shall be of value for the 

 study of the vegetation, it has to be not only practically complete 

 but moreover it must be accompanied by, or made as a part of a 

 thorough oecological and phyto-sociological investigation. 



As appears not only from notes added to the publications on 

 Krakatao but also from the very character of these publications 

 itself, the new flora of the island has never yet been investigated 

 by persons who had made a sufficient study of the flora of the 

 Dutch East Indies and were able to recognize on the spot all or 

 nearly all plants, and could consequently make out the frequency 

 of each of the species. All investigators contented themselves with 

 collecting some specimens or fragments of the species they chanced 

 to observe of which they knew at best the names and as a rule not 

 even so much; most, if not all, of the materials were named after the 

 trip was finished, as a rule at Buitenzorg. To this I would raise 

 no insurmountable objection if only in the collections made in this 

 manner every species was represented by a sufficient number of 

 forms, if subsequent collectors had always seriously studied all the 

 materials gathered by their predecessors in order to make themsel- 

 ves, as far as possible, acquainted with the flora and, finally, if they 

 had occasion of revisiting Krakatao with short intervals in order to 

 resume and extend their investigations after having worked out the 

 results of a former trip. These favourable circumstances, however, 

 have never yet coincided: during or after each new excursion it ap- 

 peared that the collectors did not know or did not recognize many 

 of the plants which had been found already at former trips and 

 often in large numbers. Moreover, not a single publication shows that 



( l Ernst, Neue Flora Vulkaninsel Krakcitau (1907), pp. 8, 46; - Doc t e is van 

 Leeuwen in Ann. |ard. Bot. Buitenzorg XXXI (1921), pp. 58, 117. 



