14 THE ORCHID REVIEW. (MARCH, 1923- 
other constituents of the present flora of Krakatau. Lycopodium cernuum L., 
and Ophioglossum moluccanum Schlecht., are both recorded for the island. 
Since these Pteridophyta have mycorrhizal fungi in their saprophytic 
subterranean prothalli, and since all the facts point to the relation between 
the two organism sbeing obligate, we are again faced with the same problem. 
It is more unlikely here even than in Orchids that inoculation has taken 
place before dissemination. 
The Leguminose on the island possibly present the clearest case of the 
separate arrival of the symbiotic organisms. As is well known practically 
all members of this family show on their roots tubercles which enclose 
masses of bacteria. ‘‘ On the roots of all the Leguminous plants examined, 
Vigna, Canavalia, Erythrina, 1 found the charactistic root-tubercles in 
abundance.” It is incredible that seedlings of these plants had their roots 
inoculated with bacteria and were then blown over. 
It is extremely probable that at the present time the soil of Krakatau is, 
from a biological point of view, very similar to what it was before the 
eruption. Treub, in his first visit in 1886, three years after the eruption, 
found pioneers of vegetation from the shore to the peak; blue-green Alge 
were the first colonists on the pumice and the volcanic ash, as also on the 
exposed blocks of rock in the ravines on the mountain slopes. The second 
visit in 1897 showed that diatoms were also present. Ernst, in 1906, found 
bacteria and moulds. ‘‘ The Bacteria and Mould-Fungi may perhaps have 
played even a more important part in the preparation of a favourable sub- 
stratum for the higher plants in the earliest phases of colonisation. 
Researches into the Bacterial flora-were first undertaken during our (the 
third) expedition ; it is, however, certain that these minute organisms were 
introduced on to the island and began to develope as soon as, and possibly 
even before, the algz and spores.” The number of bacteria present per gram 
of soil (2,200,000 the average of four samples) agrees with those found in 
the soil at Buitenzorg. Further, ‘‘ several moulds were found on the culture-' 
plate.” Though no details are given of these there can be no doubt that 
at the present day the soil of the island possesses an abundant fungus-flora, 
and it is extremely probable that mycorrhizal fungi are as common there as 
in neighbouring regions. Thus, it seems that Krakatau presents no special 
difficulties in accounting for the occurrence of Orchids. There is, however, 
still the greater problem of accounting for the distribution of Orchids in 
general, 
GHENT Exuisition.—In addition to visiting the Floralies, foreign 
excursionists will have the privilege of seeing free of charge the Chateau 
des Comtes, the Cloth Market, the Cathedral of St. Bavon, the Arch eeological 
Museum, the Botanical Garden, the ruins of the Abbey of St. Bavon, etc. 
