Lonesome Dove, Volume 2: Comanche Moon by Larry McMurtry

WHEN FAMOUS SHOES saw that the tracks of the Buffalo Horse were going straight into the Sierra Perdida, he sat down on a rock to think about it. Scull was studying a small cactus, for reasons Famous Shoes could not fathom. Very often Scull would notice a plant he was not familiar with and would stop and study it for many minutes, sometimes even sketching it in a small notebook he carried. Sometimes he would ask Famous Shoes about the plant, but often it would be a plant Famous Shoes had no use for and knew little about. Some plants were useful and many were very useful, yielding up medicines or food or, as in the case of some cactus buds, yielding up important visions. But, as with people, some plants were completely useless. When Scull stopped for a long stretch to examine some fossil in the rocks or some useless plant, Famous Shoes grew impatient.

Now he was very impatient. The little cactus Scull was studying was of no interest at all-all anyone needed to know about it was that its thorns were painful if they stuck you. Now the situation they faced was apt to be far more painful than the thorns of any cactus. They were near the country of Ahumado, the Black Vaquero, a man who had wounded Scull once and who would do worse than wound him if he took him prisoner. Scull needed to recognize that their situation was perilous. Under such circumstances, studying a cactus was not the proper behaviour for a captain.