Prickly Lettuce, a Compass Plant

Teacher’s Story

The more we know of plants, the more we admire their ways of attaining success in a world where it is only attained by a species after a long struggle. While plants may not be conscious of their own efforts for living on successfully, they have developed them just the same, and they merit our admiration perhaps even more, than as if their strategy was the result of conscious thought. The prickly lettuce has a story to tell us about success attained by the prevention of exhaustion from thirst. In fact, the success of this weed depends much upon its being able to live in dry situations and withstand the long droughts of late summer. The pale green stems grow up slim and tall, bearing leaves arranged alternately and from all sides, since between two, one of which is exactly above the other, two other leaves are borne. Thus, if the leaves stood out naturally, the shape of the whole plant would be a somewhat blunt pyramid. But during the hot, dry weather, the leaves do not stand out straight from the stem; instead, they twist about so that they are practically all in one plane, and usually point north and south, although this is not invariably the case. The way this twisting is accomplished is what interests us in this plant. The long spatulate leaf has a thick, fleshy midrib, and at the base are developed two pointed lobes which clasp the stalk. The leaf is soft and leathery and always seems succulent, because it retains its moisture; it has a ruffled edge near its base, which gives it room for turning without tearing its margin. Each leaf tips over sidewise toward the stem, and as far as necessary to bring one edge uppermost. Thus the sun cannot reach its upper surface to pump water from its tissues. The ruffled margin of the upper edge is pulled out straight when the leaf stands in this position, while the lower margin is more ruffled than ever. Thus, it stands triumphantly, turning edgewise to the sun, retaining its moisture and thriving when cultivated plants are dry and dying.

It also has another “anchor to the windward.” A plant so full of juice would prove attractive food for cattle when pastures are dry. The leaves of this perhaps escape, because each has a row of very sharp spines on the lower side of the midrib. At first we might wonder why they are thus placed; but if we watch a grazing animal, as a cow, reach out her tongue to pull the herbage into her mouth, we see that these spines are placed where they will do the most efficient work. The teasel has the same clever way of warning off meddlesome tongues. The prickly lettuce also has spines on its stem, and the leaves are toothed with spines at their points.