436 
PACIFIC EXPLORATION: D. H. CAMPBELL 
important agency is that of certain birds. He mentions specially, a 
species of plover, and the tropic bird. As is well known, Darwin brings 
out this point, having examined the mud adherent to the feet of cer- 
tain migratory birds, in which be found seeds of many kinds. A com- 
plete investigation of this topic would probably be worth while. The 
role of air and water currents as agencies in plant distribution, still 
affords a large field for investigation. 
In connection with the study of the island floras, especially those of 
the volcanic islands, it would be very desirable to have careful observa- 
tions made on the reestablishment of the vegetation on areas covered 
by recent volcanic ash or lava. Such observations, for example, as those 
made upon Krakatoa after the great eruption of 1883. It would prob- 
ably not be possible to find so complete a sterilization of a whole island 
as was then the case, but if by chance any similar occasion should arise, 
the opportunity should certainly not be lost. 
The study of the reestablishment of the vegetation on such a sterilized 
area would be of great scientific value ; and probably results quite worth 
while might be had from an investigation of the development of vegeta- 
tion on less extensive new lava flows, or areas covered with fresh vol- 
canic ash. By such studies it might be possible to determine what 
effects, if any, are produced upon plants growing in lava or ash, of differ- 
ent chemical or physical properties. 
The Pacific Coast of America, both north and south, offers many 
interesting problems, dealing with various phases of plant origin and 
distribution, and probably Cahfornia would prove the richest field for 
such studies. 
Aside from the question of variation in the native plants, and the 
reasons for the high percentage of endemism involving the question of 
mutation, etc., there are various other points to be considered. If 
California, like Hawaii, is to be looked upon as a centre of 'formative 
activity,' the reasons for this need to be carefully and thoroughly 
investigated. 
California has received additions to its flora both from the north and 
from the south; and there is much to be learned as to the means by which 
these immigrants reached California, and just where was the home 
whence they came. Thus, of the northern elements of the flora there is 
a small infusion of Asiatic and Eurasian types, such as the Tan-bark 
Oak, the Giant Equisetum, species of Fritillaria, the Sitka Spruce, 
Madrono (Arbutus), etc. Probably a thorough study of the fossil plants 
of the State will throw light on some of these questions, and a beginning 
has already been made in this direction. 
