Quatitative Study of the Entire Root Systems of Weed and Crop Plant under Field Conditions

Upon germination the embryonic plant previously dormant in the seed is released. For the first time it comes in contact with the surrounding environment through the medium of its tap or seminal roots. Normally this occurs under the surface. For several days from germination to emergence the young seedling develops rapidly in darkness without any photosynthetic process at work. During all this period the plant's roots are the only observable organs to support new life developing from the seed. To appreciate fully the significance of roots for the survival of a plant, one must recognize, that during this early embryonic development and before it emerges above the surface, its size is increased from 300 to 400 per cent. This enormously great work must be attributed almost entirely to the activity of the plant's roots. In a study made recently 2 an average root system of Marquis wheat measured at emergence 12.62 inches in a greenhouse and twice that length when grown under field conditions. The corresponding figures for Hannchen barley were 14.75 and 27 inches; for Banner oats 6.6 and 14 inches; for wild oats, Avena fatua, 6.95 and 13 inches; for Russian thistle, Salsola kali, 1.5 and 2.75 inches, and for wild mustard, Brassica arvensis, 2 and 5 inches. Any serious damage to the roots at this time invariably leads to the death of the entire plant. Thus equipped with organs for absorption of the soil solution, the plants emerge above the surface and start competing with one another as soon as their root systems begin to occupy the same feeding ground (Pavlychenko and Harrington, '35). From that time on until maturity the underground competition continues and its effects are reflected by the corresponding development of the aboveground parts. The extent of the top growth is a direct result of the causes operating underneath the surface. Root study, therefore, provides a key to a proper interpretation of the aboveground plant development. To be of full value, however, the root sys-