Page:Popular Science Monthly Volume 68.djvu/66

62 a pistillate spike, we have an eight to twenty-two-rowed ear. This accounts for the well-known fact that corn ears are even rowed.

My observations suggest to me that corn and teosinte may have had a common origin, and that in the process of evolution the cluster of pistillate spikes in teosinte were developed from the lateral branches of a tassel-like structure, while the corn ear developed from the central spike. It is probable that the progenitor of these plants was a large much-branched grass, each branch being terminated by a tassel-like structure, bearing hermaphrodite flowers. Fig. 13 is a diagram of such a plant. As evolution progressed, the central tassel came to produce only staminate flowers, these being higher and in a better position to fertilize the flowers on the lower branches. At the same time, the lateral branches came to produce only pistillate flowers, their position not being favorable as pollen producers, while, on the contrary, they were favorably placed to receive pollen. This differentiation in the flowers was accompanied by a shortening of the internodes of the lateral branches until they were entirely enclosed in the leaf sheaths, as shown in Fig. 1.

Fig. 14 is a sketch of the stalk and ears of a well-developed sweet corn plant after the removal of the leaves and leaf sheaths. It will be noted that the number of nodes in the ear-bearing branches agrees exactly with the number of nodes found in the stalk, above the point of attachment. If these branches were elongated to their normal length, we should have something similar to the diagram in Fig. 13. The lowermost branches usually arise at or below the surface of the soil. They develop their own root systems where they are in contact with the soil, and soon separate from the main plant and become independent plants bearing a proper tassel and ear, in all respects similar to the parent plant. Intermediate between the tassel-bearing branches and the first ear-bearing branches on the main stem there often may be found one or more branches, the tendencies of which seem to be about equally divided between ear-bearing and tassel-bearing, resulting in a structure combining the characteristics of both tassel and ear.