Once it was thought that a great gulf was fixed between the flowerless and the flowering plants. But further study has shown that this gulf is bridged, and that the two piers which support the bridge are the Lycopodineae (club-mosses and selag-inellas) and the gymnosperms.
After the pollen of a cone-bearer has found its way to the ovule the carpels close over and protect the developing seed. Those of the red cedars and junipers become succulent, and unite so as to form a globe with the seed inside. Those of the pine, spruce, hemlock, fir, and larch alter still more. The ovule of any of these trees is fastened to a little protruding disk in the carpel-wall (Fig. 83). After the ovule has been quickened this disk begins to develop surprisingly on its own account. It expands at top and sides, and soon completely outgrows the carpel to which it was once but an humble annex. So the carpel eventually loses its individuality and becomes two scales. The uppermost of these is the developed disk which has the seeds attached to it, and hence is called the "semeniferous," or seed-bearing, scale. The outstripped remainder of the carpel forms a "bract-scale," and both become woody and, in many cones, are glued together with resin.
The ovule of the yew has no carpel, but after the vitalizing touch of the pollen upon it the ring shaped disk about its base begins to grow, and forms a cup around the developing seed.
Though three or four of its little archegonia may have been fertilized, the seed of a native gymnosperm contains but one baby-tree. All the others were supplanted by the growth of this one, which has become sole heir, and will take to itself all the nourishment in the ripe seed. This inheritance is no mean one.
Fig. 83. - Common silver fir (Abies pectinata).
A, A young carpel, showing the protruding disk and the two ovules; B, a part of a mature cone showing the seed-bearing scales (s) and the bract scales (b); C, a ripe seed-bearing scale with the winged seeds. (After Sachs).
It has been laid away in the prothallus, whose cells are packed full of food for its nursling - albumen, starches, and fats.
And now the seed which has been so well guarded and nourished during its immaturity is to be sent out to get its own living. The red cedars, junipers, and yews employ the birds as sowers. When the cedar- and juniper-seeds are ripe the succulent globes which enclose them become purple, and show vividly against the sombre green of the boughs. At the season when there is little provender in the snow-clad fields these pretty berries tempt the birds, which devour them, and scatter their seeds broadcast. The fleshy cup which has grown up about the yew-seed becomes juicy and soft and turns bright-red. But though this cup is "pleasant to the eye and good for food," from a bird's point of view, the seed contained in it is poisonous. Instinct warns the birds of this, and after they have devoured the juicy cups they spit up the seeds, perhaps in a place far from the tree whence they were gathered.
The other cone-bearers (with the exception of the "bald"-cypress) send their offspring away by their tried old messenger, the wind. The ripe seeds are winged, and when they are ready to travel the cone-scales, which have hitherto been pressed together, draw apart, setting their wards free. The scales of the firs drop away altogether, leaving nothing of the cone but a woody axis.
The cones of the hemlocks, pines, and spruces gradually assume a pendant position while they are maturing, so that when their scales separate the ripe seeds are at once given to the winds. Thus the cone-bearers, like good parents, do their utmost "in protection of their tender ones".
But alas! In the vegetable world, no less than in the worlds of mice and men, the best-laid schemes "gang aft aglee".
For often, in latter summer, one may see a squirrel perched upon a pine-branch, holding a nearly-ripe cone between his fore-paws. With attitudes and actions like those of a little monkey he tears away the scales and flings them earthward, and meantime he feasts eagerly upon the seeds whose stores of nutriment were prepared and laid away with no foreboding of his sharp claws and nibbling teeth thrust impertinently between Nature's plans and their fulfilment.