Vot. I] STEWART—BOTANY OF THE GALAPAGOS ISLANDS 233 
where each flow of lava can be traced for a distance of several 
miles by the difference in the color of the vegetation. Similar 
conditions were noticed at Villamil on the south side of this 
island. 
Growth 
Owing to the short vegetative period on the lower and drier 
parts of the Galapagos, growth is very slow among the peren- 
nial forms, but correspondingly rapid among the annuals. 
This fact was observed especially on Chatham Island in Jan- 
uary and February. While the greater portion of the spring 
weeds were well advanced in growth at this place, in the later 
part of January, some of them were just coming through the 
ground; while upon a return to the same place, three weeks 
later, it was found that most of the latter had matured and 
dried up. In fact most of the vegetation had gone into the 
resting condition during this time, so that the change in the 
appearance of the vegetation was very striking. 
Some insight was gained into the rate of growth of the 
Opuntias at Academy Bay on Indefatigable Island. In making 
a trail into the interior in the early part of November, many 
of the smaller specimens were cut off three or four feet above 
the ground. It was found in July that many of the cut ends 
had put forth branches, some of which were as much as sixteen 
inches long. Many of the absorbing roots of Cissampelos 
Parcira were cut at the same time, and many of these had put 
forth several rootlets from the cut ends, about one sixth of an 
inch in diameter and from four to seven feet long. These 
rootlets do not seem to increase in diameter very rapidly after 
they are once formed, for the same condition was noticed on 
an old trail, on the northwest side of this island, that had not 
been touched for several years. 
ORIGIN OF THE GALAPAGOS ISLANDS 
Two different theories have been advanced to explain the 
origin of these islands. Until the appearance of Dr. Baur’s 
paper: “On the Origin of the Galapagos Islands,” * it was gen- 
erally conceded among naturalists that they were of oceanic 
origin, each island having been built up separately from all of 
the rest by volcanic activity. In this paper Dr. Baur expressed 
an entirely different view concerning their origin, basing his 
1Am. Nat. v. 25, 1891, pp. 217-229, 307-326. 
