Waiting to exhale.

“Let’s get this over with,” lamented a 10-yeara-old boy as he and his parents waited in the Desert Botanical Garden’s tour gathering area for my tour to begin on an otherwise perfect Sunday morning last winter. Thinking to myself that this could be a long 40 minutes, I reached back to my volunteer training and remembered: try to find something about the desert with which this young city-dweller can relate. While the tour group gathered, I learned that he really liked to swim, so I asked, “How long can you hold your breath underwater?” “For almost a full minute!” he proudly boasted. “That’s pretty darn good,” I replied, “but see that saguaro cactus over there? It can hold its breath all day long.” When he asked me why it does that, I sensed that his curiosity about our desert plants was perhaps growing. By how the tour group had gathered around, and I explained that plants respire or “breathe” through tiny holes or pores (by taking in carbon dioxide and releasing oxygen through stomata). Doing so during the scorching heat of a summer day, however, would result in so much loss of moisture that cacti and most other succulent plants would eventually shrivel up and die. So, unlike most other plants, many cacti and succulents close their pores all day long and only “breathe” at night when things cool down. Concerned that I might lose my audience if I added too much more detail, I avoided mentioning that the technical term for this water-efficient type of photosynthesis is Crassulacean Acid Metabolism (CAM); I suspected that jaw-breaker would likely even cause the parents’ eyes to glaze over. For those of you not prone to eye-glazing, please read on.