28 



AMERICAN HOMES AND GARDENS 



January, 1908 



New Facts About Venus' Fly-Trap 



By W. C. Purdy 



[IGOROUS plants of Dionoea, or Venus' 

 Flytrap, secured in early spring and kept 

 under glass, will put forth flowers in 

 June. The leaf or "trap" is the chief object 

 of interest; its behavior in catching insects, 

 and the pressure it exerts to retain these 

 when captured, are surprising. A brief 



description of the plant, together with results of experiments 



performed by the writer, may be acceptable to the reader. 

 At the top of a naked 10-inch stalk which arises from 



the rosette of leaves or traps, the delicate blossoms appear, 



in a compact 5 to 8 flowered cyme. The inflorescence 



is determinate. The flowers, half 



as large as apple blossoms, have five 



white spreading petals, delicately 



veined. These petals do not drop 



off when the flower withers; they 



curl inward tightly from the tip, 



gradually becoming discolored and 



brown. When the flower opens, the 



pollen is ripe, but the stigma is 



<| Traps in Natural Position. Four of the 

 Six Sensitive Hairs may be Seen in A 



undeveloped. In a day or two the 

 17 to 20 stamens (which are at 

 first closely arranged about the 

 pistil) become very divergent, thus 

 removing the ripened pollen from 

 the vicinity of the small feathery 

 stigma, which develops meantime. 

 In this manner the flower prevents 

 self-pollination. 



Looking down upon the upper surface of the trap, one 

 observes that the two halves, standing open at an angle of 

 90 degrees or more, are each convex; also that the marginal 

 bristles on one side incline toward those on the opposite side, 

 so that, when the trap is closed, these bristles intercross, as 

 the fingers do when the hands are loosely clasped. The inner 

 portion of each half of the trap is finely mottled with red. 

 From this mottled surface arise six slender hairs, three on 

 each half. These hairs are very sensitive, a touch on any one 

 of them causing the trap to close almost instantly. They 

 therefore constitute the "trigger" of the trap. When clo- 



sure is effected by some one's touching a sensitive hair with 

 an object, as a pencil, the trap will open again in a few hours; 

 but if the trap be closed by placing in it a bit of animal tissue, 

 such as meat, or if it catch an insect, several days, usually 

 four to nine, elapse before the trap opens again. 



It is not generally known that the trap in closing has two 

 distinct positions or stages, which, in the absence of better 

 terms, we may designate as first position and second position 

 respectively. When a trap closes, from any cause whatever, 

 the curvature of the sides is reversed, and the margins nearly 

 or quite touch each other, the marginal bristles intercrossing. 

 The closed trap is therefore double-convex in shape, forming 



a cavity within large enough to ac- 

 commodate the insect, if one be 

 captured. Each half of the trap de- 

 scribes a simple curve from midrib 

 to margin. This is the first position. 

 If a trap closes upon an insect, 

 or upon a bit of animal tissue, it 

 first closes to the first position, as 

 described above. But it does not 



Upper Illustration 

 JJ Flower Cluster of Dionaea. Flowers lettered in order"of?age. In 

 A, (the youngest) stigma is undeveloped. In B, stigma is developed, 

 and stamens are divergent. In C, petals are curling. In D and E, 

 petals are curled tightly and discolored 



Lower Illustration 

 fj Plants of Dionaea on Common Dinner Plate. Traps A, B, C, 

 and D have caught flies, and are in the second position. Flowers 

 are not fully opened 



•I The Trap A about Twenty Minutes 

 after Catching a Fly. The Trap is in the 

 First Position 



remain in this position while di- 

 gesting and absorbing its prey. In 

 the first position, the extreme mar- 

 gins of the trap are in contact 

 with each other, the marginal 

 bristles intercrossing. Now if the 

 closure be effected by the presence 

 of animal tissue in the trap, 

 this first position is slowly re- 

 placed by a very different one. The simple curve described 

 by each side in the first position is changed very slowly to a 

 compound curve. The two-thirds of the trap nearest the 

 midrib retains the double-convex form of the first position, 

 but the one-third nearest the margins — and including them — 

 separates and the edges curve outward, away from each 

 other, the line of contact of the two sides receding toward 

 the midrib. 



This curving outward of the margins results in two things : 

 First, the bristles, which in the first position were inter- 

 crossed, now separate and swing outward with each recurving 



