As is typical of the writings of O. Henry, "The Cactus" has a surprise ending. This surprise results because of the character trait about which Trysdale berates himself: "his fatuous and tardily mourned egoism." Having returned from the wedding of the beautiful young woman whom he had assumed he would marry, Trysdale rues his vanity and conceit. But, the irony is that he does not fully understand how this very vanity and conceit prevented his marriage. For, as Trysdale searches in his memory for where he erred, he remembers how the young woman always looked up "so childlike and worshipful," but she was always modest.
Recalling the night on which he had proposed to the beautiful woman to marry him, she had asked him about keeping quiet his knowledge of Spanish since Captain Caruthers had told her that he is fluent. Because "the incense of her admiration" was so sweet and flattering, he allowed her to retain the assumption that he knows the language. Yet, Trysdale has thought no more of this question of hers. Instead, he remembers how she seemed a "snared bird" that night. Yet, she sent no word as she had promised; and, when he saw her two nights later, she seemed "wondering, eager." Courteous, but adamantly quiet, he awaited her explanation; she gave no reply, but became cold.
Then, the voice of the other man in the room intrudes his reverie, asking him what is wrong and suggesting they have a drink. Rather distractedly, the friend sees the cactus on Trysdale's table and asks him where he got it.
"A present," said Trysdale, "from a friend. Kinow the species?"
"Here's the name on the tag," his friend replies. "Know any Spanish, Trysdale?"
"No," said Trysdale, with the bitter wraith of a smile--"Is it Spanish?"
Now, Trysdale suspects that his egoism at not admitting to not having knowledge of Spanish has been a true mistake.
Yes, explains his friend. He tells Trysdale the Spanish name is Ventomarme, which means "Come and take me" in English. Ironically, Trysdale's his pretense and egoism have been his nemesis. However, while this trick ending of O. Henry's is pathetic, it is not tragic.