Among the modern improvements in agriculture we may reckon the invention of the Seed-drill as one of the most important. By means of this invention, seed is greatly economized, the supply can be regulated, and the sower knows exactly where every grain of seed goes. There is no scattering, as in the wasteful broadcast plan, by which the seeds are flung almost at random over the field, and may or may not fall into the furrows. The Seed-drill, on the contrary, either stamps holes or ploughs narrow furrows, measures the seed into them, and in some machines replaces the earth. The former kind of machine rather deserves the name of a dibble, and was invented for the purpose of superseding the use of the hand-dibble.
It is really a pitiful thing to see human beings endowed with reason and aspirations performing such a task as dibbling by hand, one going backwards with a dibble in each hand, and the other following and putting seed into the holes. Yet the field labourers have the greatest objection to the machine dibble, as, indeed, they have to any sort of labour-saving machine, thinking that it will lessen the demand for labour, and prevent them from earning a livelihood.
I well remember how a country clergyman, pitying the hard toil of the hand-dibblers, took occasion when he visited town to purchase a machine dibble wherewith one man could set eight rows of beans at once. It was a very simple affair, comprehensible even by the dull brain of a Wiltshire labourer. His trouble was all in vain, for no one would use it, and there was such a disturbance about it in the village, that for the sake of peace its owner laid it up in a loft and abandoned its use. There might be some semblance of reason in thinking that it would deprive them of their field labour, but no cottager would even use it in his own garden, though it was freely offered to any one who wished to borrow it.
These machines have their parallels in Nature, two of which are represented in the illustration.
The lower left-hand figure represents the female Grasshopper depositing her eggs. She is furnished with a sharply pointed ovipositor, composed of two blades. When she is about to lay her eggs, she searches for a suitable piece of ground, where the earth is tolerably soft, and with the closed ovipositor bores a hole. She then separates the blades slightly, and an egg glides between them into the ground, precisely as is done by the machine dibble with its beans. When I first saw and used the instrument, some twenty-five years ago, the parallel struck me at once.
The female of the familiar Daddy Long-legs (Tipula) acts in a similar manner. She is furnished with an ovipositor too short to be used like that of the grasshopper, and so she attains her object in a rather different manner. Making use of her long stilt-like legs, she sets herself nearly upright, with the point of the ovipositor in the ground. She then twists herself from side to side, just after the principle of the bradawl, and so proceeds until she has made a hole large enough for her purpose. The blades of the ovipositor are then separated, and the egg placed in the hole, as has been described of the grasshopper.
The upper figure represents one of the large Ichneumon-flies depositing the egg in the grub of some wood-inhabiting larva. How she bores the hole has already been described when treating of Boring Tools, and the process need not again be discussed. The principal point at present is, that after the hole is bored, an egg can pass between the blades of the ovipositor, though they are but little thicker than human hairs.
One of the most extraordinary instances of this kind of ovipositor is found in an Ichneumon-fly brought from Bogotá. The body, from the head to the end of the tail, is not quite an inch long, while the ovipositor is six inches and a half in length, and scarcely thicker than that of the insect whose portrait is given in the illustration. Nothing is as yet known of its habits, so that the object of this wonderfully long ovipositor is a mystery. But that it should be used like other ovipositors is evident enough, and the chief wonder is, what are the mechanical means whereby an egg can be propelled between blades so long and slender.
There is a genus of Ichneumon-flies called Pelecinus. They deposit their eggs in wood-boring larvæ, and we might imagine that the ovipositor would be a long one. It is, however, extremely short, and the requisite length is obtained by the form of the abdomen, the joints of which are so long and narrow that they almost look as if they had passed through a wire-drawing machine, the length of the head and throat being three-eighths of an inch, and that of the abdomen an inch and a half. This long abdomen belongs only to the female, that of the male being short and club-shaped.