A Preliminary Survey of the Oenothera Organensis Population.
A Preliminary Survey of the Oenothera Organensis Population.
复制标题
月见草种群的初步调查。
作者：
S. Emerson
ENOTHERA ORGANENSIS is known solely from the one range of 0 mountains from which it takes its name. The Organ Mountains of southern New Mexico form part of a long chain lying east of and parallel to the Rio Grande. They differ from the San Andres Mountains on the north and the Franklin Mountains on the south by their greater altitude and in their volcanic origin. There has recently been published a Geology of the Organ Mountains (DUNHAM 1935) from which the accompanying map (figure I ) has been taken. The Organ Mountains occupy an area approximately eighteen miles long (north and south) and varying from three to eight miles in width, lying about fifteen miles east of Las Cruces, New Mexico. The mountains rise from a plain of four to five thousand feet elevation to a height of 9108 feet a t Organ Peak. Of the area occupied by the mountains, approximately thirty-three square miles are above the 6000 feet level and less than ten square miles above the 7000 feet level. Oenotheras have been found only at elevations above 6000 feet and only in canyons which drain relatively large areas of higher land. The canyons in which the oenotheras are found have been carved out of the solid igneous rock, rhyolite, which makes up the greater part of the mountains. Both the side walls and the floors of the canyons are for the most part very steep, so that the runoff of water after rains is extremely rapid. The rainfall in the mountains has not been measured but is perhaps not much greater than at State College, near Las Cruces, where the mean annual precipitation in a period of over seventy years is approximately eight and one-half inches. The largest amount of precipitation occurs in the summer months and generally as local thunder showers. A large part of the mountains is definitely arid, and with the exception of Filmore Canyon, which has a permanent stream, all the water courses are dry most of the time. While the canyons were being formed, however, basins were eroded in the canyon floors. These have become filled with rock and gravel and it is in these natural reservoirs that the oenotheras are found. Growing with the oenotheras in these pockets is an Aquilegia, whereas the immediate environs are occupied by such xerophytes as Yucca, Agave, Opuntia, etc. These conditions are illustrated in the photographs in figure 2. Oenotheru orgunensis, unlike the other oenotheras with angled seeds (that is, the onagras), is strictly perennial. The central axis never elongates,
