MON'OCOT'YLE'DONS (from Gk. pOvoc, monos, single -1-- tcor0V6v, koiy/(Ve1n, cup-shaped cavity, from ko(ybl, socket). One of the two great divisions of angiosperms (q.v.). The name means 'one cotyledon.' and suggests one of the distinguishing features of the group, namely that the embryo developed Within the seed has hut one cotyledon or seed-leaf ; while in the other group (dicotyledons) it. has two. The fact that the embryo has only a single cotyledon is not so significant as its position. At 011P end of the axis of the embryo the root tip is organized, while at the other end the cotyledon is developed, the stem tip coming out on the side of the axis. In dicotyledons the tips of the roots and those of the stems occupy the ends of the axis, and the cotyledons come out on the side. The most easily recognized teharaeters of the mono cotyledons, however, are as follows: Woody strands scattered in the stem, as in a corn stalk, and not forming a definite cylinder, parallel veined leaves ( not reticulately veined), and parts of the flowers in threes (never in fives or fours).
None of these characters is without exception. but their combination usually indieates a mono cotyledon, the final test being the character of the embryo. Formerly the members of the group were called `endogens,' but the name has been abandoned in this connection and is applied in a totally different way. The whole assemblage of monocotyledons numbers about 211,000 living spe cies, and among thent are some of the most conspicuous and useful of plants. As illustra tions the following prominent groups may be mentioned: Pond weeds, grasses, palms. lilies, and orchids.