. Carnegie Institution of Washington publication. 48 Guayale. base. In P. hysterophorus and P. lyratum they are very broad, and are membranous in the former. Figs. 7 and 9 will make these and other characters Fig. 9.—Achenes of (i) Parthenium argentatum, (2) P. hysterophorus, (3) P. incanum, (4) P. lyratum. SEEDLING. When germination is complete the seedling of the guayule consists of a short primary stem (hypocotyl), 5 to 10 mm. in length, terminating in a long, slender tap-root. Attempts to find the end of this in the field have been fruitless, on account of the nature of the groun
. Carnegie Institution of Washington publication. 48 Guayale. base. In P. hysterophorus and P. lyratum they are very broad, and are membranous in the former. Figs. 7 and 9 will make these and other characters Fig. 9.—Achenes of (i) Parthenium argentatum, (2) P. hysterophorus, (3) P. incanum, (4) P. lyratum. SEEDLING. When germination is complete the seedling of the guayule consists of a short primary stem (hypocotyl), 5 to 10 mm. in length, terminating in a long, slender tap-root. Attempts to find the end of this in the field have been fruitless, on account of the nature of the ground and because of its very tender character and great length and thinness. Experiments show that it reaches a depth of at least several inches. This slender root- let, with very few branches, is the means of keeping the plantlet supplied with water from the soil for some months, as frequently during the first year in the field no adequate development of lateral roots occurs. The seed leaves (cotyledons) are nearly or entirely circular in form, and range in size from mm. in width by 3 mm. in length to mm. in width and mm. in length, according to various conditions. At the apex of each cotyledon is a hydathode, composed of a group of water stomata. Other conditions being the same, seedlings grown in the shade and high relative humidity have the largest cotyledons (plate 34, figs. 6, 9), and the largest were seen on seedlings grown experimentally under such con- ditions. The primary stem is about 1 mm. in diameter, and in seedlings grown under natural conditions, , with direct sunlight, is dark red; in. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Carnegie Institution of Washington. Washington, Carnegie Institution of Washington
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