Vol.1] 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 

 Opmitias 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 

 Pareira 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 



lAm. Nat. v. 25, 1891, pp. 217-229, 307-326. 



