Algist, 1901.] 



KNOWLEDGE. 



171 



not in calm air fall until the docay of the seed-vessel or 

 the stem allowed the escape of the contents. The 

 saucer-shaped recept^ieles of many of the <'oiii/i(i<it(r 

 furnish a familiar exiUiiple. Most of the plants of the 

 Pink tribe (CaryophyUacece) have drj' capsules, which 

 open at the top when the seeds are mature, and of 

 similar structure is the fruit of the Cohimbine, the 

 Poppies, the Henbane. The fniit of the last na,med 

 consists of a woodv urn-shaped vessel, surrounded by t.he 

 enlarged calyx, and closed at the top by a beautifully 

 fashioned close-fitting lid, which, when the fruit is ripe, 

 falls off. exposing tlie seeds within. All these jilants 

 have stiff upright stems. A gust of wind or the brushing 

 past of an animal bends the stems, which spring back 

 into their upright position, and in so doing project the 

 seeds out of the seed vessel. Fruits arranged on this 

 plan have aptly been called catapult-fruits. The wind 

 similarly assists dispersal in the case of heavy-fruited 

 trees, such as the Spanish and Horse Chestnuts. It is 

 chiefly during gales that the fruit is torn from the 

 branches, and filing by the swaying boughs clear of the 

 umbrage of the parent. In these cases heavy fiiiits arc 

 a positive advantage, their momentum carrying them to 

 a gi-eater distance than a lighter body would reach. The 

 majority of wind-dispersed plants, however, work 

 towards the opposite extreme, and ensure transport by 

 means of the extreme lightness of the fruits. The 

 Orchids and Broom-rapes, for instance, produce an im- 

 mense quantity of dust^like seeds; a single seed of the 

 Lady's Tresses, Goodyera repens, is estimated to weigh no 

 more than one-five hundred thousandth of a gram. A 

 large number of other seeds or fruits, heavy in com- 

 parison with the foregoing, increase their buoyancy by 

 means of wing-like or feathery appendages, which offer 

 resistance to the air, and in consequence tend to fall 

 slowly. Sometimes the seed itself bears a membranous 

 wing. In other cases, as in the Ash, it is the envelope 

 which encloses the seed that is flattened and wing-like. 

 In the Sycamore, the wrapping of each seed is prolonged 

 on one side into a wing like the blade of a propeller, and 

 :.cts in a similar way, whirling round as the fruit falls. 

 aTid retarding its passage to the earth, so that in a high 

 wind the fruit may be carried some huudi-eds of feet. 

 Note likewise the broad-winged fruit of the Elm. Of 

 feathery appendages which serve the same purposes 

 jiumerous examples occur to the mind — the Traveller's 

 •Toy. for instance, and the Pasque Flower, Reed-mace, 

 and many grasses. The brown heads of the Reed-mace, 

 when ripe, consist of a vast number of tiny seeds, each 

 on a delicate stalk, clothed with long slender haii-s. 

 which spread as soon as they are set free, so that the 

 head fluffs out into a'mass of downy fruit of surprising 

 dimensions, which the wind carries in all directions. 

 Most perfect of all, we have the beautiful parachute 

 fruits of the Dandelion and its allies, and of some other 

 plants. In the Dandelion the seed is small and 

 cucumber-shaped. Attached to its upper end is a 

 delicate stalk, which branches in umbel-like fashion into 

 an exquisite hemispherical parachute, which represents, 

 moi-phologically, the limb or free upper portion of the 

 altered calyx. These appendages and the surrounding 

 general involucre are hygroscopic — affected by varying 

 degrees of moisture. Should rain come on before the 

 fruit is launched forth on the air, all the little umbrclla.s 

 fold up and the involucre closes round them and keeps 

 them dry. When the sun bursts forth, the whole 

 elaborate structure expands again, a breath of wind 

 severs the fruit from its slight attachment to the 

 receptacle, and away it floats. In many ca.ses the 



att<nchnient of the seed to it-s parachute is also very 

 slight, so that collision during its journey with an 

 obstacle sn.aps the connection ; the now useless para- 

 chute is cast off, and the seed dro])s, to seek some dam|) 

 crevice in the earth where it may germinate. 



Water plays a less conspicuous but not unimportant 

 part in seed-dispersal. A river is, of course, continually 

 Ijringing down seeds dropped into it from many plants 

 along its banks, and in times of flood these are spread 

 over adjoining low grounds. Tho seeds of many of the 

 plants which fringe ponds and streams fiixit, and even 

 where no current exists, arc drifted from one place to 

 another by the wind. Eventually they sink, and 

 germinate in the mud or sand which covers the bottom. 



The part, intentional or unintentional, which animals 

 take in the dissemination of seeds is nearly as important 

 as that played by the wind. Just as the brightly-coloured 

 flowers are designed to attract insect visitors, so the use 

 of .scarlet berries is to attract birds, which, by eatuig 

 them, may scatter the seed. Numerous experiments 

 have shown that the vitality of the seeds contained in 

 these juicy berries is not impaired by their passage 

 through the birds' bodies. Moreover, digestion in birds 

 is extremely rapid, and the seeds may be expelled within 

 an hour of being eaten. The bright colour and sweet 

 juiciness of the Strawberry and Cherry and Apple, then, 

 corresponds in function to the brilliant petals and store 

 of honey of the flowers ; both the plant and its animal 

 visitor reap material benefit from ^he visits of the latter, 

 and hence the relation continues, and, presumably, 

 spreads. But in most cases the plant is not so dependent 

 on the animal for the successful accomplishment of this 

 function of its existence as in the case of fertilization. 

 If no birds eat the fruit, it will fall to the ground- 

 perhaps be carried by wind or water to some distance — 

 and may there germinate. Only in a few cases are the 

 visits of birds almost indispensable. The parasitic 

 Mistletoe appears to furnish a case in point. Without 

 the presence of birds, which eat the fruit and distribute 

 the sticky rejected seeds about the branches, the chance 

 of one of the heavy smooth berries reaching and adher- 

 ing to the branch of even a neighboui-ing tree appears 

 remote indeed. The advantage to these ben7-bearing 

 plants, of fruit which will retain its juiciness, and its 

 hold on the fruit^stem, for a long period, is sufficieptly 

 obvious. Long after most of the summer plants have 

 shed their seeds, the hips and haws, the black berries of 

 the Privet and the white ones of the Snowberry, 

 brighten the bare branches, furnishing a welcome winter 

 food-supply to the birds, and thus securing a wide and 

 efficient dissemination. 



Thus far regarding fruits which lay themselves out 

 to attract animals. Many other plants effect dispersal 

 by making animals the unknowing and sometimes un- 

 willing carriers of their progeny. The fruits and seeds 

 of such plants arc usually distinguishable by the hooks 

 and barbs that they bear, tho object of which is to 

 attach the seeds to the body of passing animals. Tho 

 large heads of the Burdock, with their hooked involucre- 

 scales, are familiar to every child. Note that in this 

 cas3 it is the general involuci-e that bears the hooks. 

 When ripe the whole head, containing many compara- 

 tively heavy fruits, is detached by adherence to the wool 

 or hair of a passing animal. More often it is single 

 fruits that bear hooked bristles, or barbed hairs. Many 

 instances occur in oiu- commoner plants — examine, for 

 instance, the fruits of the Bur-Marigold, the Agrimony, 

 Enchanter's Nightshade, Hound's-tongue. How effective 

 a means of dis.scmination these hooked fruits furnish is 



