PECULIAR SEEDS

Evening Star, Issue 21742, 9 June 1934, Page 10

PECULIAR SEEDS

BRAZIL NUTS’ STRUGGLE FOR EXISTENCE During the war some strange fruits were picked up in Limehouse after an air raid (writes an English correspondent). They were sent by the Home Office to the Pharmaceutical Society for examination, and thence to Kcw in order that their species might be determined. In this way they came to the notice of Sir Arthur Hill, the Director of Kew’ Gardens, and stimulated his interest in the structure of fruits and' seeds. He recently gave a fascinating lecture to the Royal Institution on the remarkable behaviour of embryos of germinating seeds, especially those that escape from hard shells such as'plum stones. Seeds vary immensely in the degree of their protection by outer coatings or shells. The shells of Brazil nuts are, as it were, only the seeds’ lighter underwear. The nuts are borne in a spherical woody ball about six inches in diameter,. with a wall half an inch thick which is as hard as well-seasoned oak and has a smooth glass-like inner layer. AL one end there is a firmly plugged hole about half an inch in diameter. This natural bomb-shell can bo broken only by a blow from a heavy hammer or by cutting with a saw. It usually contains • fifteen to twenty of the Tints. When the conditions for germination are suitable all of the kernels begin to germinate simultaneously. As the ball is tightly packed there ia little room for expansion by growth, so the kernels have to escape from inside the ball. The half-inch hole is their only route of egress. So a mortal struggle occurs between the nuts for access to the hole. Only one out of the fifteen or twenty is successful, and occupies it. The seeds in all the other nuts die. WATTLES BORN IN FIRE. There is a great variation in the resistance of different sorts of seeds to germination. The seeds of willows and poplars germinate the day after they are sown, and if kept for a few days they lose their power of germination. Compare this delicacy with the toughness of the seeds of Australian wattles, which require fire to stimulate them'towards the fuller life, for they rarely, germinate- unless a fire has passed over and scorched the ground in which -they are living. In order to make ’wattle seeds germinate in England- their tough coats have to bo

scraped with a file or treated with sulphuric acid. Experiments have recently been •made with old seeds from the Museum at Kew, Seeds of Anthyllis vulneria and Trifolium striatum, both ninety years old, ! have been successfully germinated, and also seeds of the Spanish broom (Cytisus scoparius) eighty-one years old. Sir Arthur 1 remarked that the late Sir Michael Foster once showed him a pot of Iris in which the seed was beginning to germinate fourteen years after it was sown.

The -embryos, of dates, coconuts, and double coconuts have a peculiar method of escaping from their stony sheaths. The date solves they problem by growing a tube out of its stone, through which the embryo is transported. The embryo continues to obtain nourishment through the tube from the seed, and afterwards bursts out of the tube to start independent existence in the surrounding soil. Sir Arthur compares these tubes with the cloth tubes used as escapes by persons caught in the upper storeys of a burning house. In plums, cherries, almonds, and olives the walls of the stone are botanically part of the fruit. The seed is the kernel inside the walls. Such stones consist of two similar halves cemented together by the plant. There are no connecting cells across the joint. The stones are easily split into two halves by the pressure of the growing embry > when the cement along, the joint has been sufficiently moistened. CRUISING SEEDS,

Not all seeds leave the plant before they begin to germinate. The mangrove is ' viviparous, and its seeds begin \to germinate while the fruit still hangs on the tree. The shoots grfaw downwards and develop into a young plant which drops off ou to the water, floats upright, and drifts until it settles on a mud flat in a tropical estuary, The ' Madagascar plant, Typhonodorum grows well-developed young offspring in a similar manner. These drop'on to the water still attached to the large bean-like seeds, and sail off upright with the young leaves in the air.

In the vegetable marrow the young seedling develops a special sort of lever for forcing open the seed case. In other plants a plug is forced out of a capsule, as a cork out of a champagne bottle. The fruit of the mare’s tail (Hippuris) behaves in this way. The Nigerian blood plum has a furnished with double doors for releasing the embryo. If the flesh is stripped from the stone a lid is found at one end. The lid splits into a pair of doors that open outwards when pressed by the growing embryo. The seed of the Queensland Burdekin plum is almost as well protected as that of a Brazil nut. The middle sheath of the fruit, which in ordinary plums is the fleshy part, is stony, so that the seed has two tough coats. This strong, double shell is about an inch in diameter, and contains twelve seeds, only one of which will probably survive. What is the explanation of the origin of structures, such as the shells of Brazil nuts and Burdekin plums, which cause the death of over 90 per cent, of the enclosed seeds? Can it be protection? Why should some unprotected seeds, such as those of orchids and lilies, papery and almost transparent, be able to live dormant for long periods and then germinate successfully? The evolutionary significance of much of the structure and behaviour of Jiving organisms, including plants, remains obscure.