The Distribution of the Hepaticce. 2 i 1 
ocean barriers that separate the regions where they now occur, as 
the spores are not of the type that could be carried long distances 
without perishing. Since there are no connecting forms in the higher 
latitudes that could explain the passage of these forms from one 
tropical zone to the other, we can only assume that these genera 
are the little changed descendants of ancient widely distributed 
types. 
The ready distribution of Ferns, by means of their spores, has 
often been cited, but with these, as with Hepaticae, there are great 
differences as to the ease of distribution. Ferns with thick-walled 
colourless spores are readily disseminated, as the spores retain their 
power of germination for many months, or even years. But there 
are other ferns, such as the Hymenophyllaceae and Osmunda, whose 
spores quickly perish unless they immediately have the conditions 
necessary for germination. We know, however, from the fossil 
record, that both the Hymenophyllaceae and Osmundaceae are old 
types, and their present wide distribution is readily accounted for 
by this assumption. These ferns may very well be compared with 
the Hepaticae of wide distribution whose spores are not fitted for 
extended dissemination. 
An admirable opportunity for studying on a large scale the 
relative adaptability of plants for rapid distribution, has been 
offered by the island of Krakatau, which, as is well known, was 
practically entirely denuded of all vegetation by the great eruption 
of 1883. Since that time a number of visits have been made from 
Buitenzorg to the island, and the gradual re-establishment of the 
vegetation has been carefully noted. Last year (April, 1906), the 
writer had an opportunity of visiting Krakatau, and observing the 
present condition of the vegetation. The island is now quite 
covered with plants, including many trees of considerable size. 
Owing to the limited time at our disposal and the difficulties of 
cutting a way through the dense growth of tall grasses that cover 
most of the lower land between the shore and the central volcanic 
cone of the island, our observations were necessarily confined to 
the region near the shore, where there is a narrow belt of woods. 
When the island was first visited about three years after the 
eruption (Treub, Ann. du Jardin botanique de Buitenzorg, VII., 
1888), eleven species of ferns had already established themselves, as 
well as a number of flowering plants with easily carried seeds and 
fruits, such as several grasses and Composite. At the present time 
several species of Orchids are abundant, as well as many grasses 
