There is a saying that a mountain is high enough to reach the rhododendron and befaria limit, in the same way one says one has reached the snow limit. In employing this expression it is tacitly assumed that under identical temperatures a certain kind of vegetation must grow. This is not strictly true. The pines of Mexico are absent in the Peruvian Andes. The Caracas La Silla is not covered with the same oaks that flourish in New Granada at the same height. Identity of forms suggests an analogy of climate, but in similar climates the species may be very diversified.