Elementary botany . em of classification adopted by some,the angiosperms form a group. The group angiosperms is thendivided into two classes, the monocotyledones and dicotyledones.(It should be remembered that all systematists do not agree inassigning the same grade and limits to the classes, subclasses,etc. For example, some treat of the angiosperms as a class,and the monocotyledons and dicotyledons as subclasses; whileothers would divide the monocotyledons and dicotyledons intoclasses, instead of treating each one as a class or as a differ also in usage as to the termin
Elementary botany . em of classification adopted by some,the angiosperms form a group. The group angiosperms is thendivided into two classes, the monocotyledones and dicotyledones.(It should be remembered that all systematists do not agree inassigning the same grade and limits to the classes, subclasses,etc. For example, some treat of the angiosperms as a class,and the monocotyledons and dicotyledons as subclasses; whileothers would divide the monocotyledons and dicotyledons intoclasses, instead of treating each one as a class or as a differ also in usage as to the termination of theordinal name; for example, some use the word Liliales for Lilii-florce, in writing of the order.) 937. Monocotyledones.—In the monocotyledons there is asingle cotyledon on the embryo; the leaves are parallel veined;the parts of the flower are usually in threes; endosperm is usu-ally present in the seed; the vascular bundles are usually closed,and are scattered irregularly through the stem as shown by a. Fig. 497- A. Cross-section of the stem of an oak tree thirty-seven years old, showing theannual rings, rm, the medullary rays; m, the pith (medulla). B. Cross-sectionof the stem of a palm tree, showing the scattered bundles. cross-section of the stem of a palm (fig. 497), or by the arrange-ment of the bundles in the corn stem (fig. 57). Thus a singlecharacter is not sufficient to show relationship in the class (nor ORDER, CLASS, GROUP. 491 is it in orders, nor in many of the lower grades), but one mustuse the sum of several important characters. 938. Dicotyledones.— In the dicotyledons there are twocotyledons on the embryo; the venation of the leaves is reticu-late; the endosperm is usually absent in the seed; the parts of theflower are frequently in fives; the vascular bundles of the stemare generally open and arranged in rings around the stem, as shownin the cross-section of the oak (fig. 497). There are exceptionsto all the above characters, and the sum of the
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Keywords: ., bookauthoratk, bookcentury1900, bookdecade1900, booksubjectbotany
